diff --git a/src/lib/3rdparty/lineedit.h b/src/lib/3rdparty/lineedit.h
index 7f19ada8f..3e6dcf0f3 100644
--- a/src/lib/3rdparty/lineedit.h
+++ b/src/lib/3rdparty/lineedit.h
@@ -92,7 +92,7 @@ public:
         SelectAll = 8
     };
 
-    LineEdit(QWidget* parent = 0);
+    LineEdit(QWidget* parent = nullptr);
 
     void addWidget(QWidget* widget, WidgetPosition position);
     void removeWidget(QWidget* widget);
@@ -152,7 +152,7 @@ Q_SIGNALS:
     void sizeHintChanged();
 
 public:
-    SideWidget(QWidget* parent = 0);
+    SideWidget(QWidget* parent = nullptr);
 
 protected:
     bool event(QEvent* event) override;
diff --git a/src/lib/3rdparty/squeezelabelv1.h b/src/lib/3rdparty/squeezelabelv1.h
index 4835bc535..1e781b92f 100644
--- a/src/lib/3rdparty/squeezelabelv1.h
+++ b/src/lib/3rdparty/squeezelabelv1.h
@@ -42,7 +42,7 @@ class FALKON_EXPORT SqueezeLabelV1 : public QLabel
     Q_OBJECT
 
 public:
-    SqueezeLabelV1(QWidget* parent = 0);
+    SqueezeLabelV1(QWidget* parent = nullptr);
 
 protected:
     void paintEvent(QPaintEvent* event) override;
diff --git a/src/lib/adblock/adblockaddsubscriptiondialog.h b/src/lib/adblock/adblockaddsubscriptiondialog.h
index 9d78d5799..fa73b1866 100644
--- a/src/lib/adblock/adblockaddsubscriptiondialog.h
+++ b/src/lib/adblock/adblockaddsubscriptiondialog.h
@@ -33,7 +33,7 @@ class FALKON_EXPORT AdBlockAddSubscriptionDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit AdBlockAddSubscriptionDialog(QWidget* parent = 0);
+    explicit AdBlockAddSubscriptionDialog(QWidget* parent = nullptr);
     ~AdBlockAddSubscriptionDialog();
 
     QString title() const;
diff --git a/src/lib/adblock/adblocktreewidget.h b/src/lib/adblock/adblocktreewidget.h
index a2c040a35..4045eda66 100644
--- a/src/lib/adblock/adblocktreewidget.h
+++ b/src/lib/adblock/adblocktreewidget.h
@@ -28,7 +28,7 @@ class FALKON_EXPORT AdBlockTreeWidget : public TreeWidget
 {
     Q_OBJECT
 public:
-    explicit AdBlockTreeWidget(AdBlockSubscription* subscription, QWidget* parent = 0);
+    explicit AdBlockTreeWidget(AdBlockSubscription* subscription, QWidget* parent = nullptr);
 
     AdBlockSubscription* subscription() const;
 
diff --git a/src/lib/app/mainmenu.h b/src/lib/app/mainmenu.h
index 8fa5115f5..447f65adc 100644
--- a/src/lib/app/mainmenu.h
+++ b/src/lib/app/mainmenu.h
@@ -36,7 +36,7 @@ class FALKON_EXPORT MainMenu : public QMenu
     Q_OBJECT
 
 public:
-    explicit MainMenu(BrowserWindow* window, QWidget* parent = 0);
+    explicit MainMenu(BrowserWindow* window, QWidget* parent = nullptr);
 
 
     void initMenuBar(QMenuBar* menuBar) const;
diff --git a/src/lib/autofill/passwordbackends/databaseencryptedpasswordbackend.h b/src/lib/autofill/passwordbackends/databaseencryptedpasswordbackend.h
index 202e54e1f..048f37399 100644
--- a/src/lib/autofill/passwordbackends/databaseencryptedpasswordbackend.h
+++ b/src/lib/autofill/passwordbackends/databaseencryptedpasswordbackend.h
@@ -101,7 +101,7 @@ class MasterPasswordDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit MasterPasswordDialog(DatabaseEncryptedPasswordBackend* backend, QWidget* parent = 0);
+    explicit MasterPasswordDialog(DatabaseEncryptedPasswordBackend* backend, QWidget* parent = nullptr);
     ~MasterPasswordDialog();
 
     void delayedExec();
@@ -128,7 +128,7 @@ class AskMasterPassword : public QDialog
     Q_OBJECT
 
 public:
-    explicit AskMasterPassword(DatabaseEncryptedPasswordBackend* backend, QWidget* parent = 0);
+    explicit AskMasterPassword(DatabaseEncryptedPasswordBackend* backend, QWidget* parent = nullptr);
 
 private Q_SLOTS:
     void verifyPassword();
diff --git a/src/lib/bookmarks/bookmarksexport/bookmarksexportdialog.h b/src/lib/bookmarks/bookmarksexport/bookmarksexportdialog.h
index 21d9a4447..5c83f49a3 100644
--- a/src/lib/bookmarks/bookmarksexport/bookmarksexportdialog.h
+++ b/src/lib/bookmarks/bookmarksexport/bookmarksexportdialog.h
@@ -34,7 +34,7 @@ class FALKON_EXPORT BookmarksExportDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit BookmarksExportDialog(QWidget* parent = 0);
+    explicit BookmarksExportDialog(QWidget* parent = nullptr);
     ~BookmarksExportDialog();
 
 private Q_SLOTS:
diff --git a/src/lib/bookmarks/bookmarksicon.h b/src/lib/bookmarks/bookmarksicon.h
index 3b234ab54..f4b7ce21e 100644
--- a/src/lib/bookmarks/bookmarksicon.h
+++ b/src/lib/bookmarks/bookmarksicon.h
@@ -30,7 +30,7 @@ class FALKON_EXPORT BookmarksIcon : public ClickableLabel
 {
     Q_OBJECT
 public:
-    explicit BookmarksIcon(QWidget* parent = 0);
+    explicit BookmarksIcon(QWidget* parent = nullptr);
 
     void setWebView(WebView* view);
     void checkBookmark(const QUrl &url, bool forceCheck = false);
diff --git a/src/lib/bookmarks/bookmarksimport/bookmarksimportdialog.h b/src/lib/bookmarks/bookmarksimport/bookmarksimportdialog.h
index 502be35b4..0fda61ec9 100644
--- a/src/lib/bookmarks/bookmarksimport/bookmarksimportdialog.h
+++ b/src/lib/bookmarks/bookmarksimport/bookmarksimportdialog.h
@@ -36,7 +36,7 @@ class FALKON_EXPORT BookmarksImportDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit BookmarksImportDialog(QWidget* parent = 0);
+    explicit BookmarksImportDialog(QWidget* parent = nullptr);
     ~BookmarksImportDialog();
 
 private Q_SLOTS:
diff --git a/src/lib/bookmarks/bookmarksmanager.h b/src/lib/bookmarks/bookmarksmanager.h
index b2c0e10d9..ad154daef 100644
--- a/src/lib/bookmarks/bookmarksmanager.h
+++ b/src/lib/bookmarks/bookmarksmanager.h
@@ -39,7 +39,7 @@ class FALKON_EXPORT BookmarksManager : public QWidget
     Q_OBJECT
 
 public:
-    explicit BookmarksManager(BrowserWindow* window, QWidget* parent = 0);
+    explicit BookmarksManager(BrowserWindow* window, QWidget* parent = nullptr);
     ~BookmarksManager();
 
     void setMainWindow(BrowserWindow* window);
diff --git a/src/lib/bookmarks/bookmarksmenu.h b/src/lib/bookmarks/bookmarksmenu.h
index bf52e7277..c38699ecc 100644
--- a/src/lib/bookmarks/bookmarksmenu.h
+++ b/src/lib/bookmarks/bookmarksmenu.h
@@ -31,7 +31,7 @@ class FALKON_EXPORT BookmarksMenu : public Menu
     Q_OBJECT
 
 public:
-    explicit BookmarksMenu(QWidget* parent = 0);
+    explicit BookmarksMenu(QWidget* parent = nullptr);
 
     void setMainWindow(BrowserWindow* window);
 
diff --git a/src/lib/bookmarks/bookmarkstoolbar.h b/src/lib/bookmarks/bookmarkstoolbar.h
index 2fed35934..294fb2d23 100644
--- a/src/lib/bookmarks/bookmarkstoolbar.h
+++ b/src/lib/bookmarks/bookmarkstoolbar.h
@@ -34,7 +34,7 @@ class FALKON_EXPORT BookmarksToolbar : public QWidget
 {
     Q_OBJECT
 public:
-    explicit BookmarksToolbar(BrowserWindow* window, QWidget* parent = 0);
+    explicit BookmarksToolbar(BrowserWindow* window, QWidget* parent = nullptr);
 
 private Q_SLOTS:
     void contextMenuRequested(const QPoint &pos);
diff --git a/src/lib/bookmarks/bookmarkstoolbarbutton.h b/src/lib/bookmarks/bookmarkstoolbarbutton.h
index c28bbcdfc..8e34dbd68 100644
--- a/src/lib/bookmarks/bookmarkstoolbarbutton.h
+++ b/src/lib/bookmarks/bookmarkstoolbarbutton.h
@@ -31,7 +31,7 @@ class FALKON_EXPORT BookmarksToolbarButton : public QPushButton
     Q_OBJECT
 
 public:
-    explicit BookmarksToolbarButton(BookmarkItem* bookmark, QWidget* parent = 0);
+    explicit BookmarksToolbarButton(BookmarkItem* bookmark, QWidget* parent = nullptr);
 
     BookmarkItem* bookmark() const;
     void setMainWindow(BrowserWindow* window);
diff --git a/src/lib/bookmarks/bookmarkstools.h b/src/lib/bookmarks/bookmarkstools.h
index 8f9ff3bf7..6408bf187 100644
--- a/src/lib/bookmarks/bookmarkstools.h
+++ b/src/lib/bookmarks/bookmarkstools.h
@@ -31,7 +31,7 @@ class FALKON_EXPORT BookmarksFoldersMenu : public QMenu
     Q_OBJECT
 
 public:
-    explicit BookmarksFoldersMenu(QWidget* parent = 0);
+    explicit BookmarksFoldersMenu(QWidget* parent = nullptr);
 
     BookmarkItem* selectedFolder() const;
 
diff --git a/src/lib/bookmarks/bookmarkstreeview.h b/src/lib/bookmarks/bookmarkstreeview.h
index fe52f9fbe..80b662599 100644
--- a/src/lib/bookmarks/bookmarkstreeview.h
+++ b/src/lib/bookmarks/bookmarkstreeview.h
@@ -37,7 +37,7 @@ public:
         BookmarksSidebarViewType
     };
 
-    explicit BookmarksTreeView(QWidget* parent = 0);
+    explicit BookmarksTreeView(QWidget* parent = nullptr);
 
     ViewType viewType() const;
     void setViewType(ViewType type);
diff --git a/src/lib/bookmarks/bookmarkswidget.h b/src/lib/bookmarks/bookmarkswidget.h
index aa319d8cf..aa8733919 100644
--- a/src/lib/bookmarks/bookmarkswidget.h
+++ b/src/lib/bookmarks/bookmarkswidget.h
@@ -37,7 +37,7 @@ class FALKON_EXPORT BookmarksWidget : public LocationBarPopup
 {
     Q_OBJECT
 public:
-    explicit BookmarksWidget(WebView* view, BookmarkItem* bookmark, QWidget* parent = 0);
+    explicit BookmarksWidget(WebView* view, BookmarkItem* bookmark, QWidget* parent = nullptr);
     ~BookmarksWidget();
 
 private Q_SLOTS:
diff --git a/src/lib/downloads/downloadmanager.h b/src/lib/downloads/downloadmanager.h
index f31649e54..7cde467f4 100644
--- a/src/lib/downloads/downloadmanager.h
+++ b/src/lib/downloads/downloadmanager.h
@@ -59,7 +59,7 @@ public:
         }
     };
 
-    explicit DownloadManager(QWidget* parent = 0);
+    explicit DownloadManager(QWidget* parent = nullptr);
     ~DownloadManager();
 
     void loadSettings();
diff --git a/src/lib/downloads/downloadoptionsdialog.h b/src/lib/downloads/downloadoptionsdialog.h
index bce57afec..f16059bcf 100644
--- a/src/lib/downloads/downloadoptionsdialog.h
+++ b/src/lib/downloads/downloadoptionsdialog.h
@@ -36,7 +36,7 @@ class FALKON_EXPORT DownloadOptionsDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit DownloadOptionsDialog(const QString &fileName, QWebEngineDownloadItem *downloadItem, QWidget* parent = 0);
+    explicit DownloadOptionsDialog(const QString &fileName, QWebEngineDownloadItem *downloadItem, QWidget* parent = nullptr);
     ~DownloadOptionsDialog();
 
     void showExternalManagerOption(bool show);
diff --git a/src/lib/history/historymanager.h b/src/lib/history/historymanager.h
index 65284a476..6dc21ea1e 100644
--- a/src/lib/history/historymanager.h
+++ b/src/lib/history/historymanager.h
@@ -38,7 +38,7 @@ class FALKON_EXPORT HistoryManager : public QWidget
     Q_OBJECT
 
 public:
-    explicit HistoryManager(BrowserWindow* window, QWidget* parent = 0);
+    explicit HistoryManager(BrowserWindow* window, QWidget* parent = nullptr);
     ~HistoryManager();
 
     void setMainWindow(BrowserWindow* window);
diff --git a/src/lib/history/historymenu.h b/src/lib/history/historymenu.h
index 34af164d1..23bef2916 100644
--- a/src/lib/history/historymenu.h
+++ b/src/lib/history/historymenu.h
@@ -30,7 +30,7 @@ class FALKON_EXPORT HistoryMenu : public Menu
     Q_OBJECT
 
 public:
-    explicit HistoryMenu(QWidget* parent = 0);
+    explicit HistoryMenu(QWidget* parent = nullptr);
 
     void setMainWindow(BrowserWindow* window);
 
diff --git a/src/lib/history/historytreeview.h b/src/lib/history/historytreeview.h
index 77cb37594..fca396043 100644
--- a/src/lib/history/historytreeview.h
+++ b/src/lib/history/historytreeview.h
@@ -33,7 +33,7 @@ public:
         HistorySidebarViewType
     };
 
-    explicit HistoryTreeView(QWidget* parent = 0);
+    explicit HistoryTreeView(QWidget* parent = nullptr);
 
     ViewType viewType() const;
     void setViewType(ViewType type);
diff --git a/src/lib/navigation/downicon.h b/src/lib/navigation/downicon.h
index 9f1de17ba..42239558b 100644
--- a/src/lib/navigation/downicon.h
+++ b/src/lib/navigation/downicon.h
@@ -24,7 +24,7 @@
 class FALKON_EXPORT DownIcon : public ClickableLabel
 {
 public:
-    explicit DownIcon(QWidget* parent = 0);
+    explicit DownIcon(QWidget* parent = nullptr);
 
 private:
     void contextMenuEvent(QContextMenuEvent* ev) override;
diff --git a/src/lib/navigation/goicon.h b/src/lib/navigation/goicon.h
index 4e350024d..470f0bc90 100644
--- a/src/lib/navigation/goicon.h
+++ b/src/lib/navigation/goicon.h
@@ -24,7 +24,7 @@
 class FALKON_EXPORT GoIcon : public ClickableLabel
 {
 public:
-    explicit GoIcon(QWidget* parent = 0);
+    explicit GoIcon(QWidget* parent = nullptr);
 
 private:
     void contextMenuEvent(QContextMenuEvent* ev) override;
diff --git a/src/lib/navigation/navigationcontainer.h b/src/lib/navigation/navigationcontainer.h
index 41e7e6c8f..6a0bd406b 100644
--- a/src/lib/navigation/navigationcontainer.h
+++ b/src/lib/navigation/navigationcontainer.h
@@ -29,7 +29,7 @@ class TabBar;
 class FALKON_EXPORT NavigationContainer : public QWidget
 {
 public:
-    explicit NavigationContainer(QWidget* parent = 0);
+    explicit NavigationContainer(QWidget* parent = nullptr);
 
     void addWidget(QWidget* widget);
     void setTabBar(TabBar* tabBar);
diff --git a/src/lib/navigation/reloadstopbutton.h b/src/lib/navigation/reloadstopbutton.h
index 4dca9a2ad..923e35569 100644
--- a/src/lib/navigation/reloadstopbutton.h
+++ b/src/lib/navigation/reloadstopbutton.h
@@ -28,7 +28,7 @@ class FALKON_EXPORT ReloadStopButton : public ToolButton
     Q_OBJECT
 
 public:
-    explicit ReloadStopButton(QWidget* parent = 0);
+    explicit ReloadStopButton(QWidget* parent = nullptr);
 
     void showStopButton();
     void showReloadButton();
diff --git a/src/lib/navigation/websearchbar.h b/src/lib/navigation/websearchbar.h
index 7f3c4bab8..0e9dacdd0 100644
--- a/src/lib/navigation/websearchbar.h
+++ b/src/lib/navigation/websearchbar.h
@@ -38,7 +38,7 @@ class OpenSearchEngine;
 class FALKON_EXPORT WebSearchBar_Button : public ClickableLabel
 {
 public:
-    explicit WebSearchBar_Button(QWidget* parent = 0);
+    explicit WebSearchBar_Button(QWidget* parent = nullptr);
 
 private:
     void contextMenuEvent(QContextMenuEvent* event) override;
diff --git a/src/lib/network/sslerrordialog.h b/src/lib/network/sslerrordialog.h
index d8c8070a8..df406a35a 100644
--- a/src/lib/network/sslerrordialog.h
+++ b/src/lib/network/sslerrordialog.h
@@ -36,7 +36,7 @@ class FALKON_EXPORT SslErrorDialog : public QDialog
 public:
     enum Result { Yes, No, OnlyForThisSession, NoForThisSession };
 
-    explicit SslErrorDialog(QWidget* parent = 0);
+    explicit SslErrorDialog(QWidget* parent = nullptr);
     ~SslErrorDialog();
 
     void setText(const QString &text);
diff --git a/src/lib/opensearch/editsearchengine.h b/src/lib/opensearch/editsearchengine.h
index f4f58b201..b3cd234b2 100644
--- a/src/lib/opensearch/editsearchengine.h
+++ b/src/lib/opensearch/editsearchengine.h
@@ -31,7 +31,7 @@ class FALKON_EXPORT EditSearchEngine : public QDialog
 {
     Q_OBJECT
 public:
-    explicit EditSearchEngine(const QString &title, QWidget* parent = 0);
+    explicit EditSearchEngine(const QString &title, QWidget* parent = nullptr);
 
     void setName(const QString &name);
     void setUrl(const QString &url);
diff --git a/src/lib/opensearch/searchenginesdialog.h b/src/lib/opensearch/searchenginesdialog.h
index f774a4c72..e6bbf5a2a 100644
--- a/src/lib/opensearch/searchenginesdialog.h
+++ b/src/lib/opensearch/searchenginesdialog.h
@@ -35,7 +35,7 @@ class FALKON_EXPORT SearchEnginesDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit SearchEnginesDialog(QWidget* parent = 0);
+    explicit SearchEnginesDialog(QWidget* parent = nullptr);
     ~SearchEnginesDialog();
 
 public Q_SLOTS:
diff --git a/src/lib/other/aboutdialog.h b/src/lib/other/aboutdialog.h
index a881a69f1..032cbb5e7 100644
--- a/src/lib/other/aboutdialog.h
+++ b/src/lib/other/aboutdialog.h
@@ -32,7 +32,7 @@ class FALKON_EXPORT AboutDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit AboutDialog(QWidget* parent = 0);
+    explicit AboutDialog(QWidget* parent = nullptr);
     ~AboutDialog();
 
 private Q_SLOTS:
diff --git a/src/lib/other/browsinglibrary.h b/src/lib/other/browsinglibrary.h
index 2789191dd..43aa9cdce 100644
--- a/src/lib/other/browsinglibrary.h
+++ b/src/lib/other/browsinglibrary.h
@@ -35,7 +35,7 @@ class FALKON_EXPORT BrowsingLibrary : public QWidget
     Q_OBJECT
 
 public:
-    explicit BrowsingLibrary(BrowserWindow* window, QWidget* parent = 0);
+    explicit BrowsingLibrary(BrowserWindow* window, QWidget* parent = nullptr);
     ~BrowsingLibrary();
 
     void showHistory(BrowserWindow* window);
diff --git a/src/lib/other/checkboxdialog.h b/src/lib/other/checkboxdialog.h
index 9f2f3fc24..faba4b66e 100644
--- a/src/lib/other/checkboxdialog.h
+++ b/src/lib/other/checkboxdialog.h
@@ -27,7 +27,7 @@ class FALKON_EXPORT CheckBoxDialog : public QMessageBox
 {
     Q_OBJECT
 public:
-    explicit CheckBoxDialog(const QMessageBox::StandardButtons &buttons, QWidget* parent = 0);
+    explicit CheckBoxDialog(const QMessageBox::StandardButtons &buttons, QWidget* parent = nullptr);
 
     void setCheckBoxText(const QString &text);
 
diff --git a/src/lib/other/clearprivatedata.h b/src/lib/other/clearprivatedata.h
index 537ff9663..e17c94fd1 100644
--- a/src/lib/other/clearprivatedata.h
+++ b/src/lib/other/clearprivatedata.h
@@ -31,7 +31,7 @@ class FALKON_EXPORT ClearPrivateData : public QDialog
 {
     Q_OBJECT
 public:
-    explicit ClearPrivateData(QWidget* parent = 0);
+    explicit ClearPrivateData(QWidget* parent = nullptr);
 
     static void clearLocalStorage();
     static void clearWebDatabases();
diff --git a/src/lib/other/iconchooser.h b/src/lib/other/iconchooser.h
index ce785ed0e..58589fb9f 100644
--- a/src/lib/other/iconchooser.h
+++ b/src/lib/other/iconchooser.h
@@ -35,7 +35,7 @@ class FALKON_EXPORT IconChooser : public QDialog
     Q_OBJECT
 
 public:
-    explicit IconChooser(QWidget* parent = 0);
+    explicit IconChooser(QWidget* parent = nullptr);
     ~IconChooser();
 
     QIcon getIcon();
@@ -51,7 +51,7 @@ private:
 class FALKON_EXPORT IconChooserDelegate : public QStyledItemDelegate
 {
 public:
-    explicit IconChooserDelegate(QWidget* parent = 0);
+    explicit IconChooserDelegate(QWidget* parent = nullptr);
 
     void paint(QPainter* painter, const QStyleOptionViewItem &option, const QModelIndex &index) const override;
     QSize sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const override;
diff --git a/src/lib/other/licenseviewer.h b/src/lib/other/licenseviewer.h
index 2ccb47771..01bfb0ec3 100644
--- a/src/lib/other/licenseviewer.h
+++ b/src/lib/other/licenseviewer.h
@@ -29,7 +29,7 @@ class FALKON_EXPORT LicenseViewer : public QWidget
     Q_OBJECT
 
 public:
-    explicit LicenseViewer(QWidget* parent = 0);
+    explicit LicenseViewer(QWidget* parent = nullptr);
 
     void setLicenseFile(const QString &fileName);
     void setText(const QString &text);
diff --git a/src/lib/other/siteinfowidget.h b/src/lib/other/siteinfowidget.h
index fe2cdb4a6..c38a28a1d 100644
--- a/src/lib/other/siteinfowidget.h
+++ b/src/lib/other/siteinfowidget.h
@@ -34,7 +34,7 @@ class FALKON_EXPORT SiteInfoWidget : public LocationBarPopup
 {
     Q_OBJECT
 public:
-    explicit SiteInfoWidget(BrowserWindow* window, QWidget* parent = 0);
+    explicit SiteInfoWidget(BrowserWindow* window, QWidget* parent = nullptr);
     ~SiteInfoWidget();
 
 private:
diff --git a/src/lib/popupwindow/popuplocationbar.cpp b/src/lib/popupwindow/popuplocationbar.cpp
index b4b67ce4e..aed2b3b40 100644
--- a/src/lib/popupwindow/popuplocationbar.cpp
+++ b/src/lib/popupwindow/popuplocationbar.cpp
@@ -27,7 +27,7 @@
 class FALKON_EXPORT PopupSiteIcon : public QWidget
 {
 public:
-    explicit PopupSiteIcon(QWidget* parent = 0) : QWidget(parent) { }
+    explicit PopupSiteIcon(QWidget* parent = nullptr) : QWidget(parent) { }
     void setIcon(const QIcon &icon) {
         m_icon = QIcon(icon.pixmap(16));
         update();
diff --git a/src/lib/popupwindow/popuplocationbar.h b/src/lib/popupwindow/popuplocationbar.h
index 031cf0261..1b50eee43 100644
--- a/src/lib/popupwindow/popuplocationbar.h
+++ b/src/lib/popupwindow/popuplocationbar.h
@@ -36,7 +36,7 @@ class FALKON_EXPORT PopupLocationBar : public LineEdit
     Q_PROPERTY(int fixedheight READ height WRITE setFixedHeight)
 
 public:
-    explicit PopupLocationBar(QWidget* parent = 0);
+    explicit PopupLocationBar(QWidget* parent = nullptr);
 
     void setView(PopupWebView* view);
 
diff --git a/src/lib/popupwindow/popupwebview.h b/src/lib/popupwindow/popupwebview.h
index f06b0312b..8a6169502 100644
--- a/src/lib/popupwindow/popupwebview.h
+++ b/src/lib/popupwindow/popupwebview.h
@@ -31,7 +31,7 @@ class FALKON_EXPORT PopupWebView : public WebView
 {
     Q_OBJECT
 public:
-    explicit PopupWebView(QWidget* parent = 0);
+    explicit PopupWebView(QWidget* parent = nullptr);
 
     QWidget* overlayWidget() override;
     void loadInNewTab(const LoadRequest &req, Qz::NewTabPositionFlags position) override;
diff --git a/src/lib/preferences/acceptlanguage.h b/src/lib/preferences/acceptlanguage.h
index 2bae62ed2..0b460747a 100644
--- a/src/lib/preferences/acceptlanguage.h
+++ b/src/lib/preferences/acceptlanguage.h
@@ -33,7 +33,7 @@ class FALKON_EXPORT AcceptLanguage : public QDialog
     Q_OBJECT
 
 public:
-    explicit AcceptLanguage(QWidget* parent = 0);
+    explicit AcceptLanguage(QWidget* parent = nullptr);
     ~AcceptLanguage();
 
     static QStringList defaultLanguage();
diff --git a/src/lib/preferences/autofillmanager.h b/src/lib/preferences/autofillmanager.h
index 02b96da0f..c297fc75b 100644
--- a/src/lib/preferences/autofillmanager.h
+++ b/src/lib/preferences/autofillmanager.h
@@ -34,7 +34,7 @@ class FALKON_EXPORT AutoFillManager : public QWidget
     Q_OBJECT
 
 public:
-    explicit AutoFillManager(QWidget* parent = 0);
+    explicit AutoFillManager(QWidget* parent = nullptr);
     ~AutoFillManager();
 
     void showExceptions();
diff --git a/src/lib/preferences/jsoptions.h b/src/lib/preferences/jsoptions.h
index 3593086d0..b4f84140e 100644
--- a/src/lib/preferences/jsoptions.h
+++ b/src/lib/preferences/jsoptions.h
@@ -33,7 +33,7 @@ class FALKON_EXPORT JsOptions : public QDialog
     Q_OBJECT
 
 public:
-    explicit JsOptions(QWidget* parent = 0);
+    explicit JsOptions(QWidget* parent = nullptr);
     ~JsOptions();
 
 public Q_SLOTS:
diff --git a/src/lib/preferences/pluginsmanager.h b/src/lib/preferences/pluginsmanager.h
index 81db9c29b..06c0b5a3a 100644
--- a/src/lib/preferences/pluginsmanager.h
+++ b/src/lib/preferences/pluginsmanager.h
@@ -34,7 +34,7 @@ class FALKON_EXPORT PluginsManager : public QWidget
     Q_OBJECT
 
 public:
-    explicit PluginsManager(QWidget* parent = 0);
+    explicit PluginsManager(QWidget* parent = nullptr);
     ~PluginsManager();
 
     void load();
diff --git a/src/lib/preferences/useragentdialog.h b/src/lib/preferences/useragentdialog.h
index 3125a9483..1c6a444b9 100644
--- a/src/lib/preferences/useragentdialog.h
+++ b/src/lib/preferences/useragentdialog.h
@@ -35,7 +35,7 @@ class FALKON_EXPORT UserAgentDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit UserAgentDialog(QWidget* parent = 0);
+    explicit UserAgentDialog(QWidget* parent = nullptr);
     ~UserAgentDialog();
 
 private Q_SLOTS:
diff --git a/src/lib/sidebar/bookmarkssidebar.h b/src/lib/sidebar/bookmarkssidebar.h
index 57ec44cf5..499ea96f9 100644
--- a/src/lib/sidebar/bookmarkssidebar.h
+++ b/src/lib/sidebar/bookmarkssidebar.h
@@ -36,7 +36,7 @@ class FALKON_EXPORT BookmarksSidebar : public QWidget
     Q_OBJECT
 
 public:
-    explicit BookmarksSidebar(BrowserWindow* window, QWidget* parent = 0);
+    explicit BookmarksSidebar(BrowserWindow* window, QWidget* parent = nullptr);
     ~BookmarksSidebar();
 
 private Q_SLOTS:
diff --git a/src/lib/sidebar/historysidebar.h b/src/lib/sidebar/historysidebar.h
index 643e6e818..3de85ab74 100644
--- a/src/lib/sidebar/historysidebar.h
+++ b/src/lib/sidebar/historysidebar.h
@@ -35,7 +35,7 @@ class FALKON_EXPORT HistorySideBar : public QWidget
     Q_OBJECT
 
 public:
-    explicit HistorySideBar(BrowserWindow* window, QWidget* parent = 0);
+    explicit HistorySideBar(BrowserWindow* window, QWidget* parent = nullptr);
     ~HistorySideBar();
 
 private Q_SLOTS:
diff --git a/src/lib/tabwidget/combotabbar.h b/src/lib/tabwidget/combotabbar.h
index 885cca297..c06dda6da 100644
--- a/src/lib/tabwidget/combotabbar.h
+++ b/src/lib/tabwidget/combotabbar.h
@@ -57,7 +57,7 @@ public:
         AfterTab
     };
 
-    explicit ComboTabBar(QWidget* parent = 0);
+    explicit ComboTabBar(QWidget* parent = nullptr);
 
     int addTab(const QString &text);
     int addTab(const QIcon &icon, const QString &text);
@@ -296,7 +296,7 @@ class FALKON_EXPORT TabScrollBar : public QScrollBar
 {
     Q_OBJECT
 public:
-    explicit TabScrollBar(QWidget* parent = 0);
+    explicit TabScrollBar(QWidget* parent = nullptr);
     ~TabScrollBar();
 
     bool isScrolling() const;
@@ -312,7 +312,7 @@ class FALKON_EXPORT TabBarScrollWidget : public QWidget
 {
     Q_OBJECT
 public:
-    explicit TabBarScrollWidget(QTabBar* tabBar, QWidget* parent = 0);
+    explicit TabBarScrollWidget(QTabBar* tabBar, QWidget* parent = nullptr);
 
     QTabBar* tabBar();
     QScrollArea* scrollArea();
diff --git a/src/lib/tabwidget/tabicon.h b/src/lib/tabwidget/tabicon.h
index 5dce255ec..25fd86cfa 100644
--- a/src/lib/tabwidget/tabicon.h
+++ b/src/lib/tabwidget/tabicon.h
@@ -39,7 +39,7 @@ public:
         QPixmap audioPlayingPixmap;
         QPixmap audioMutedPixmap;
     };
-    explicit TabIcon(QWidget* parent = 0);
+    explicit TabIcon(QWidget* parent = nullptr);
 
     void setWebTab(WebTab* tab);
     void updateIcon();
diff --git a/src/lib/tabwidget/tabstackedwidget.h b/src/lib/tabwidget/tabstackedwidget.h
index e2cc6f99a..babffa6c6 100644
--- a/src/lib/tabwidget/tabstackedwidget.h
+++ b/src/lib/tabwidget/tabstackedwidget.h
@@ -33,7 +33,7 @@ class FALKON_EXPORT TabStackedWidget : public QWidget
 {
     Q_OBJECT
 public:
-    explicit TabStackedWidget(QWidget* parent = 0);
+    explicit TabStackedWidget(QWidget* parent = nullptr);
     ~TabStackedWidget();
 
     ComboTabBar* tabBar();
diff --git a/src/lib/tabwidget/tabwidget.h b/src/lib/tabwidget/tabwidget.h
index 698c9a853..896cc2e0f 100644
--- a/src/lib/tabwidget/tabwidget.h
+++ b/src/lib/tabwidget/tabwidget.h
@@ -53,7 +53,7 @@ class FALKON_EXPORT MenuTabs : public QMenu
 {
     Q_OBJECT
 public:
-    explicit MenuTabs(QWidget* parent = 0) : QMenu(parent) {}
+    explicit MenuTabs(QWidget* parent = nullptr) : QMenu(parent) {}
 
 Q_SIGNALS:
     void closeTab(int);
diff --git a/src/lib/tools/animatedwidget.h b/src/lib/tools/animatedwidget.h
index 1c67845d1..24f7b7ff1 100644
--- a/src/lib/tools/animatedwidget.h
+++ b/src/lib/tools/animatedwidget.h
@@ -30,7 +30,7 @@ class FALKON_EXPORT AnimatedWidget : public QWidget
 public:
     enum Direction { Down, Up };
 
-    explicit AnimatedWidget(const Direction &direction = Down, int duration = 300, QWidget* parent = 0);
+    explicit AnimatedWidget(const Direction &direction = Down, int duration = 300, QWidget* parent = nullptr);
 
     QWidget* widget() { return m_widget; }
 
diff --git a/src/lib/tools/buttonwithmenu.h b/src/lib/tools/buttonwithmenu.h
index 6b1ab91f7..c548e8e65 100644
--- a/src/lib/tools/buttonwithmenu.h
+++ b/src/lib/tools/buttonwithmenu.h
@@ -53,7 +53,7 @@ public:
         }
     };
 
-    explicit ButtonWithMenu(QWidget* parent = 0);
+    explicit ButtonWithMenu(QWidget* parent = nullptr);
     ~ButtonWithMenu();
 
     void addItem(const Item &item);
diff --git a/src/lib/tools/certificateinfowidget.h b/src/lib/tools/certificateinfowidget.h
index a0c78d5b3..aa33098d8 100644
--- a/src/lib/tools/certificateinfowidget.h
+++ b/src/lib/tools/certificateinfowidget.h
@@ -32,7 +32,7 @@ class QSslCertificate;
 class FALKON_EXPORT CertificateInfoWidget : public QWidget
 {
 public:
-    explicit CertificateInfoWidget(const QSslCertificate &cert, QWidget* parent = 0);
+    explicit CertificateInfoWidget(const QSslCertificate &cert, QWidget* parent = nullptr);
     ~CertificateInfoWidget();
 
     // Qt5 compatibility
diff --git a/src/lib/tools/clickablelabel.h b/src/lib/tools/clickablelabel.h
index 1db10bc0b..9c5b445c0 100644
--- a/src/lib/tools/clickablelabel.h
+++ b/src/lib/tools/clickablelabel.h
@@ -35,7 +35,7 @@ class FALKON_EXPORT ClickableLabel : public QLabel
     Q_PROPERTY(QIcon fallbackIcon READ fallbackIcon WRITE setFallbackIcon)
 
 public:
-    explicit ClickableLabel(QWidget* parent = 0);
+    explicit ClickableLabel(QWidget* parent = nullptr);
 
     QString themeIcon() const;
     void setThemeIcon(const QString &name);
diff --git a/src/lib/tools/docktitlebarwidget.h b/src/lib/tools/docktitlebarwidget.h
index 4a6f0260a..2910871c8 100644
--- a/src/lib/tools/docktitlebarwidget.h
+++ b/src/lib/tools/docktitlebarwidget.h
@@ -26,7 +26,7 @@
 class FALKON_EXPORT DockTitleBarWidget : public QWidget, public Ui_DockTitleBarWidget
 {
 public:
-    explicit DockTitleBarWidget(const QString &title, QWidget* parent = 0);
+    explicit DockTitleBarWidget(const QString &title, QWidget* parent = nullptr);
     ~DockTitleBarWidget();
 
     void setTitle(const QString &title);
diff --git a/src/lib/tools/enhancedmenu.h b/src/lib/tools/enhancedmenu.h
index 6ff8267a3..75219dfd3 100644
--- a/src/lib/tools/enhancedmenu.h
+++ b/src/lib/tools/enhancedmenu.h
@@ -29,8 +29,8 @@ class FALKON_EXPORT Menu : public QMenu
 {
     Q_OBJECT
 public:
-    explicit Menu(QWidget* parent = 0);
-    explicit Menu(const QString &title, QWidget* parent = 0);
+    explicit Menu(QWidget* parent = nullptr);
+    explicit Menu(const QString &title, QWidget* parent = nullptr);
 
     // Default is false, menu will NOT be closed on middle click
     bool closeOnMiddleClick() const;
diff --git a/src/lib/tools/focusselectlineedit.h b/src/lib/tools/focusselectlineedit.h
index e387e88ea..451a2cd34 100644
--- a/src/lib/tools/focusselectlineedit.h
+++ b/src/lib/tools/focusselectlineedit.h
@@ -26,7 +26,7 @@ class FALKON_EXPORT FocusSelectLineEdit : public QLineEdit
 {
     Q_OBJECT
 public:
-    explicit FocusSelectLineEdit(QWidget* parent = 0);
+    explicit FocusSelectLineEdit(QWidget* parent = nullptr);
 
 public Q_SLOTS:
     void setFocus();
diff --git a/src/lib/tools/horizontallistwidget.h b/src/lib/tools/horizontallistwidget.h
index 0ccfe475f..31b67dfb8 100644
--- a/src/lib/tools/horizontallistwidget.h
+++ b/src/lib/tools/horizontallistwidget.h
@@ -23,7 +23,7 @@
 class HorizontalListWidget : public QListWidget
 {
 public:
-    explicit HorizontalListWidget(QWidget* parent = 0);
+    explicit HorizontalListWidget(QWidget* parent = nullptr);
 
 private:
     void mousePressEvent(QMouseEvent* event) override;
diff --git a/src/lib/tools/html5permissions/html5permissionsdialog.h b/src/lib/tools/html5permissions/html5permissionsdialog.h
index b3d8c8f71..000831c68 100644
--- a/src/lib/tools/html5permissions/html5permissionsdialog.h
+++ b/src/lib/tools/html5permissions/html5permissionsdialog.h
@@ -32,7 +32,7 @@ class HTML5PermissionsDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit HTML5PermissionsDialog(QWidget* parent = 0);
+    explicit HTML5PermissionsDialog(QWidget* parent = nullptr);
     ~HTML5PermissionsDialog();
 
     void showFeaturePermissions(QWebEnginePage::Feature feature);
diff --git a/src/lib/tools/mactoolbutton.h b/src/lib/tools/mactoolbutton.h
index 9ac797c1a..89e413df1 100644
--- a/src/lib/tools/mactoolbutton.h
+++ b/src/lib/tools/mactoolbutton.h
@@ -30,7 +30,7 @@ class FALKON_EXPORT MacToolButton : public QPushButton
     Q_PROPERTY(bool autoRaise READ autoRaise WRITE setAutoRaise)
 
 public:
-    explicit MacToolButton(QWidget* parent = 0);
+    explicit MacToolButton(QWidget* parent = nullptr);
 
     void setIconSize(const QSize &size);
 
@@ -49,7 +49,7 @@ class FALKON_EXPORT MacToolButton : public QToolButton
     Q_OBJECT
 
 public:
-    explicit MacToolButton(QWidget* parent = 0);
+    explicit MacToolButton(QWidget* parent = nullptr);
 };
 #endif
 #endif // MACTOOLBUTTON_H
diff --git a/src/lib/tools/progressbar.h b/src/lib/tools/progressbar.h
index 66a8412b0..02c9ccf3f 100644
--- a/src/lib/tools/progressbar.h
+++ b/src/lib/tools/progressbar.h
@@ -28,7 +28,7 @@ class FALKON_EXPORT ProgressBar : public QWidget
 {
     Q_OBJECT
 public:
-    explicit ProgressBar(QWidget* parent = 0);
+    explicit ProgressBar(QWidget* parent = nullptr);
 
 public Q_SLOTS:
     void setValue(int value);
diff --git a/src/lib/tools/toolbutton.h b/src/lib/tools/toolbutton.h
index fe0e2d8fb..f19ba5051 100644
--- a/src/lib/tools/toolbutton.h
+++ b/src/lib/tools/toolbutton.h
@@ -36,7 +36,7 @@ class FALKON_EXPORT ToolButton : public QToolButton
     Q_PROPERTY(QIcon fallbackIcon READ fallbackIcon WRITE setFallbackIcon)
 
 public:
-    explicit ToolButton(QWidget* parent = 0);
+    explicit ToolButton(QWidget* parent = nullptr);
 
     // MultiIcon - Image containing pixmaps for all button states
     QImage multiIcon() const;
diff --git a/src/lib/tools/treewidget.h b/src/lib/tools/treewidget.h
index ad9b50810..8a1f5ce59 100644
--- a/src/lib/tools/treewidget.h
+++ b/src/lib/tools/treewidget.h
@@ -26,7 +26,7 @@ class FALKON_EXPORT TreeWidget : public QTreeWidget
 {
     Q_OBJECT
 public:
-    explicit TreeWidget(QWidget* parent = 0);
+    explicit TreeWidget(QWidget* parent = nullptr);
     enum ItemShowMode { ItemsCollapsed = 0, ItemsExpanded = 1 };
     ItemShowMode defaultItemShowMode() { return m_showMode; }
     void setDefaultItemShowMode(ItemShowMode mode) { m_showMode = mode; }
diff --git a/src/lib/webengine/webview.h b/src/lib/webengine/webview.h
index 9893e798b..d44063886 100644
--- a/src/lib/webengine/webview.h
+++ b/src/lib/webengine/webview.h
@@ -34,7 +34,7 @@ class FALKON_EXPORT WebView : public QWebEngineView
     Q_OBJECT
 
 public:
-    explicit WebView(QWidget* parent = 0);
+    explicit WebView(QWidget* parent = nullptr);
     ~WebView();
 
     QIcon icon(bool allowNull = false) const;
diff --git a/src/lib/webtab/searchtoolbar.h b/src/lib/webtab/searchtoolbar.h
index 437a55a85..e5b3541be 100644
--- a/src/lib/webtab/searchtoolbar.h
+++ b/src/lib/webtab/searchtoolbar.h
@@ -39,7 +39,7 @@ class FALKON_EXPORT SearchToolBar : public QWidget
 {
     Q_OBJECT
 public:
-    explicit SearchToolBar(WebView* view, QWidget* parent = 0);
+    explicit SearchToolBar(WebView* view, QWidget* parent = nullptr);
     ~SearchToolBar();
 
     void showMinimalInPopupWindow();