diff --git a/autotests/cookiestest.h b/autotests/cookiestest.h
index 3014b463c..452b498e8 100644
--- a/autotests/cookiestest.h
+++ b/autotests/cookiestest.h
@@ -30,7 +30,7 @@ public:
     {
     }
 
-    bool matchDomain(QString cookieDomain, QString siteDomain) const
+    bool matchDomain(const QString &cookieDomain, const QString &siteDomain) const
     {
         return CookieJar::matchDomain(cookieDomain, siteDomain);
     }
diff --git a/src/lib/bookmarks/bookmarkstreeview.h b/src/lib/bookmarks/bookmarkstreeview.h
index 109173f55..f7f63e8f0 100644
--- a/src/lib/bookmarks/bookmarkstreeview.h
+++ b/src/lib/bookmarks/bookmarkstreeview.h
@@ -64,7 +64,7 @@ Q_SIGNALS:
     // Context menu signal with point mapped to global
     void contextMenuRequested(const QPoint &point);
     // If all bookmarks have been deselected, items is empty
-    void bookmarksSelected(QList<BookmarkItem*> items);
+    void bookmarksSelected(const QList<BookmarkItem*> &items);
 
 private Q_SLOTS:
     void indexExpanded(const QModelIndex &parent);
diff --git a/src/lib/opensearch/searchenginesdialog.cpp b/src/lib/opensearch/searchenginesdialog.cpp
index 7f6f7375b..9659c02f8 100644
--- a/src/lib/opensearch/searchenginesdialog.cpp
+++ b/src/lib/opensearch/searchenginesdialog.cpp
@@ -170,7 +170,7 @@ SearchEngine SearchEnginesDialog::getEngine(QTreeWidgetItem* item)
     return item->data(0, EngineRole).value<SearchEngine>();
 }
 
-void SearchEnginesDialog::setEngine(QTreeWidgetItem* item, SearchEngine engine)
+void SearchEnginesDialog::setEngine(QTreeWidgetItem* item, const SearchEngine &engine)
 {
     QVariant v;
     v.setValue<SearchEngine>(engine);
diff --git a/src/lib/opensearch/searchenginesdialog.h b/src/lib/opensearch/searchenginesdialog.h
index 0a4bc7bc6..f774a4c72 100644
--- a/src/lib/opensearch/searchenginesdialog.h
+++ b/src/lib/opensearch/searchenginesdialog.h
@@ -58,7 +58,7 @@ private:
     bool isDefaultEngine(QTreeWidgetItem* item);
     SearchEngine getEngine(QTreeWidgetItem* item);
 
-    void setEngine(QTreeWidgetItem* item, SearchEngine engine);
+    void setEngine(QTreeWidgetItem* item, const SearchEngine &engine);
     void changeItemToDefault(QTreeWidgetItem* item, bool isDefault);
 
     void reloadEngines();
diff --git a/src/lib/plugins/qml/api/cookies/qmlcookies.cpp b/src/lib/plugins/qml/api/cookies/qmlcookies.cpp
index 79e1621a0..5fa931d88 100644
--- a/src/lib/plugins/qml/api/cookies/qmlcookies.cpp
+++ b/src/lib/plugins/qml/api/cookies/qmlcookies.cpp
@@ -33,7 +33,7 @@ QmlCookies::QmlCookies(QObject *parent)
         emit changed(map);
     });
 
-    connect(mApp->cookieJar(), &CookieJar::cookieRemoved, this, [this](QNetworkCookie network_cookie){
+    connect(mApp->cookieJar(), &CookieJar::cookieRemoved, this, [this](const QNetworkCookie &network_cookie){
         QmlCookie *cookie = QmlStaticData::instance().getCookie(network_cookie);
         QVariantMap map;
         map.insert(QSL("cookie"), QVariant::fromValue(cookie));
diff --git a/src/lib/plugins/qml/api/fileutils/qmlfileutils.cpp b/src/lib/plugins/qml/api/fileutils/qmlfileutils.cpp
index f1e59c463..5d5d799aa 100644
--- a/src/lib/plugins/qml/api/fileutils/qmlfileutils.cpp
+++ b/src/lib/plugins/qml/api/fileutils/qmlfileutils.cpp
@@ -22,7 +22,7 @@
 #include <QDebug>
 #include <QQmlEngine>
 
-QmlFileUtils::QmlFileUtils(QString filePath, QObject *parent)
+QmlFileUtils::QmlFileUtils(const QString &filePath, QObject *parent)
     : QObject(parent)
 {
     m_path = filePath;
diff --git a/src/lib/plugins/qml/api/fileutils/qmlfileutils.h b/src/lib/plugins/qml/api/fileutils/qmlfileutils.h
index eb7969e90..3eec5b075 100644
--- a/src/lib/plugins/qml/api/fileutils/qmlfileutils.h
+++ b/src/lib/plugins/qml/api/fileutils/qmlfileutils.h
@@ -26,7 +26,7 @@ class QmlFileUtils : public QObject
 {
     Q_OBJECT
 public:
-    explicit QmlFileUtils(QString filePath, QObject *parent = nullptr);
+    explicit QmlFileUtils(const QString &filePath, QObject *parent = nullptr);
     /**
      * @brief Get the path of the file within the plugin directory.
      *        If the filePath provided is resolved to be outside the plugin
diff --git a/src/lib/plugins/qml/api/history/qmlhistory.cpp b/src/lib/plugins/qml/api/history/qmlhistory.cpp
index 06dd5f612..f6f0786ca 100644
--- a/src/lib/plugins/qml/api/history/qmlhistory.cpp
+++ b/src/lib/plugins/qml/api/history/qmlhistory.cpp
@@ -25,12 +25,12 @@
 QmlHistory::QmlHistory(QObject *parent)
     : QObject(parent)
 {
-    connect(mApp->history(), &History::historyEntryAdded, this, [this](HistoryEntry entry){
+    connect(mApp->history(), &History::historyEntryAdded, this, [this](const HistoryEntry &entry){
         QmlHistoryItem *historyItem = QmlStaticData::instance().getHistoryItem(entry);
         emit visited(historyItem);
     });
 
-    connect(mApp->history(), &History::historyEntryDeleted, this, [this](HistoryEntry entry){
+    connect(mApp->history(), &History::historyEntryDeleted, this, [this](const HistoryEntry &entry){
         QmlHistoryItem *historyItem = QmlStaticData::instance().getHistoryItem(entry);
         emit visitRemoved(historyItem);
     });
diff --git a/src/lib/plugins/qml/api/history/qmlhistoryitem.cpp b/src/lib/plugins/qml/api/history/qmlhistoryitem.cpp
index 853a3dfe2..2c4ce16ab 100644
--- a/src/lib/plugins/qml/api/history/qmlhistoryitem.cpp
+++ b/src/lib/plugins/qml/api/history/qmlhistoryitem.cpp
@@ -18,7 +18,7 @@
 #include "qmlhistoryitem.h"
 #include <QQmlEngine>
 
-QmlHistoryItem::QmlHistoryItem(HistoryEntry entry, QObject *parent)
+QmlHistoryItem::QmlHistoryItem(const HistoryEntry &entry, QObject *parent)
     : QObject(parent)
     , m_entry(entry)
 {
diff --git a/src/lib/plugins/qml/api/history/qmlhistoryitem.h b/src/lib/plugins/qml/api/history/qmlhistoryitem.h
index b43c624b4..37ae7129a 100644
--- a/src/lib/plugins/qml/api/history/qmlhistoryitem.h
+++ b/src/lib/plugins/qml/api/history/qmlhistoryitem.h
@@ -52,7 +52,7 @@ class QmlHistoryItem : public QObject
      */
     Q_PROPERTY(QDateTime lastVisitTime READ lastVisitTime CONSTANT)
 public:
-    explicit QmlHistoryItem(HistoryEntry entry, QObject *parent = nullptr);
+    explicit QmlHistoryItem(const HistoryEntry &entry, QObject *parent = nullptr);
 
 private:
     HistoryEntry m_entry;
diff --git a/src/lib/plugins/qml/qmlstaticdata.cpp b/src/lib/plugins/qml/qmlstaticdata.cpp
index 5ebf23dcb..d7a0457fa 100644
--- a/src/lib/plugins/qml/qmlstaticdata.cpp
+++ b/src/lib/plugins/qml/qmlstaticdata.cpp
@@ -78,7 +78,7 @@ QmlCookie *QmlStaticData::getCookie(const QNetworkCookie &cookie)
     return qmlCookie;
 }
 
-QmlHistoryItem *QmlStaticData::getHistoryItem(HistoryEntry entry)
+QmlHistoryItem *QmlStaticData::getHistoryItem(const HistoryEntry &entry)
 {
     QmlHistoryItem *item = m_historyItems.value(entry);
     if (!item) {
diff --git a/src/lib/plugins/qml/qmlstaticdata.h b/src/lib/plugins/qml/qmlstaticdata.h
index 83dda99a4..7a7a1050e 100644
--- a/src/lib/plugins/qml/qmlstaticdata.h
+++ b/src/lib/plugins/qml/qmlstaticdata.h
@@ -52,7 +52,7 @@ public:
     static QmlStaticData &instance();
     QmlBookmarkTreeNode *getBookmarkTreeNode(BookmarkItem *item);
     QmlCookie *getCookie(const QNetworkCookie &cookie);
-    QmlHistoryItem *getHistoryItem(HistoryEntry entry);
+    QmlHistoryItem *getHistoryItem(const HistoryEntry &entry);
     QmlTab *getTab(WebTab *webTab);
     QmlMostVisitedUrl *getMostVisitedUrl(const QString &title = QString(), const QString &url = QString());
     QmlWindow *getWindow(BrowserWindow *window);
diff --git a/src/lib/tools/qztools.cpp b/src/lib/tools/qztools.cpp
index f876aa200..499b22503 100644
--- a/src/lib/tools/qztools.cpp
+++ b/src/lib/tools/qztools.cpp
@@ -745,7 +745,7 @@ bool QzTools::matchDomain(const QString &pattern, const QString &domain)
     return index > 0 && domain[index - 1] == QLatin1Char('.');
 }
 
-QKeySequence QzTools::actionShortcut(QKeySequence shortcut, QKeySequence fallBack, QKeySequence shortcutRtl, QKeySequence fallbackRtl)
+QKeySequence QzTools::actionShortcut(const QKeySequence &shortcut, const QKeySequence &fallBack, const QKeySequence &shortcutRtl, const QKeySequence &fallbackRtl)
 {
     if (QApplication::isRightToLeft() && (!shortcutRtl.isEmpty() || !fallbackRtl.isEmpty()))
         return shortcutRtl.isEmpty() ? fallbackRtl : shortcutRtl;
diff --git a/src/lib/tools/qztools.h b/src/lib/tools/qztools.h
index 1187eec2a..f6cbeb5a9 100644
--- a/src/lib/tools/qztools.h
+++ b/src/lib/tools/qztools.h
@@ -83,7 +83,7 @@ public:
     static QString getSaveFileName(const QString &name, QWidget* parent = 0, const QString &caption = QString(), const QString &dir = QString(), const QString &filter = QString(), QString* selectedFilter = 0, QFileDialog::Options options = 0);
 
     static bool matchDomain(const QString &pattern, const QString &domain);
-    static QKeySequence actionShortcut(QKeySequence shortcut, QKeySequence fallBack, QKeySequence shortcutRtl = QKeySequence(), QKeySequence fallbackRtl = QKeySequence());
+    static QKeySequence actionShortcut(const QKeySequence &shortcut, const QKeySequence &fallBack, const QKeySequence &shortcutRtl = QKeySequence(), const QKeySequence &fallbackRtl = QKeySequence());
 
     static QString operatingSystem();
     static QString cpuArchitecture();
diff --git a/src/lib/webtab/tabbedwebview.h b/src/lib/webtab/tabbedwebview.h
index 9ee0414a7..8e896487d 100644
--- a/src/lib/webtab/tabbedwebview.h
+++ b/src/lib/webtab/tabbedwebview.h
@@ -57,7 +57,7 @@ public:
 
 Q_SIGNALS:
     void wantsCloseTab(int);
-    void ipChanged(QString);
+    void ipChanged(const QString&);
 
 public Q_SLOTS:
     void setAsCurrentTab();
diff --git a/src/plugins/FlashCookieManager/fcm_plugin.cpp b/src/plugins/FlashCookieManager/fcm_plugin.cpp
index 5a2a20ac6..2bda706ef 100644
--- a/src/plugins/FlashCookieManager/fcm_plugin.cpp
+++ b/src/plugins/FlashCookieManager/fcm_plugin.cpp
@@ -398,7 +398,7 @@ void FCM_Plugin::loadFlashCookies(QString path)
     }
 }
 
-void FCM_Plugin::insertFlashCookie(QString path)
+void FCM_Plugin::insertFlashCookie(const QString &path)
 {
     QFile solFile(path);
     if (!solFile.open(QFile::ReadOnly)) {
diff --git a/src/plugins/FlashCookieManager/fcm_plugin.h b/src/plugins/FlashCookieManager/fcm_plugin.h
index 37abb97d3..afe92a6de 100644
--- a/src/plugins/FlashCookieManager/fcm_plugin.h
+++ b/src/plugins/FlashCookieManager/fcm_plugin.h
@@ -81,7 +81,7 @@ private:
     AbstractButtonInterface* createStatusBarIcon(BrowserWindow* mainWindow);
     void loadFlashCookies();
     void loadFlashCookies(QString path);
-    void insertFlashCookie(QString path);
+    void insertFlashCookie(const QString &path);
     QString extractOriginFrom(const QString &path);
     bool isBlacklisted(const FlashCookie &flashCookie);
     bool isWhitelisted(const FlashCookie &flashCookie);
diff --git a/src/plugins/MouseGestures/3rdparty/adv_recognizer.cpp b/src/plugins/MouseGestures/3rdparty/adv_recognizer.cpp
index 3db9b0465..ccec6a4ed 100644
--- a/src/plugins/MouseGestures/3rdparty/adv_recognizer.cpp
+++ b/src/plugins/MouseGestures/3rdparty/adv_recognizer.cpp
@@ -116,7 +116,7 @@ void RealTimeMouseGestureRecognizer::addPoint(int x, int y)
 }
 
 struct DirectionSort {
-    bool operator()(GestureDefinition a, GestureDefinition b) {
+    bool operator()(const GestureDefinition &a, const GestureDefinition &b) {
         return a.directions.size() > b.directions.size();
     }
 };
diff --git a/src/plugins/TabManager/tabmanagerwidget.cpp b/src/plugins/TabManager/tabmanagerwidget.cpp
index 516e84d95..23d972d79 100644
--- a/src/plugins/TabManager/tabmanagerwidget.cpp
+++ b/src/plugins/TabManager/tabmanagerwidget.cpp
@@ -880,7 +880,7 @@ QStringList TabTreeWidget::mimeTypes() const
     return types;
 }
 
-QMimeData *TabTreeWidget::mimeData(const QList<QTreeWidgetItem*> items) const
+QMimeData *TabTreeWidget::mimeData(const QList<QTreeWidgetItem*> &items) const
 {
     QMimeData* mimeData = new QMimeData();
     QByteArray encodedData;
diff --git a/src/plugins/TabManager/tabmanagerwidget.h b/src/plugins/TabManager/tabmanagerwidget.h
index 68dbac829..2c5ce202d 100644
--- a/src/plugins/TabManager/tabmanagerwidget.h
+++ b/src/plugins/TabManager/tabmanagerwidget.h
@@ -44,7 +44,7 @@ public:
 
     Qt::DropActions supportedDropActions() const;
     QStringList mimeTypes() const;
-    QMimeData* mimeData(const QList<QTreeWidgetItem*> items) const;
+    QMimeData* mimeData(const QList<QTreeWidgetItem*> &items) const;
     bool dropMimeData(QTreeWidgetItem *parent, int index, const QMimeData *data, Qt::DropAction action);
 
     void setEnableDragTabs(bool enable);
diff --git a/src/plugins/VerticalTabs/tabtreeview.cpp b/src/plugins/VerticalTabs/tabtreeview.cpp
index 422ee3047..c2168e1c9 100644
--- a/src/plugins/VerticalTabs/tabtreeview.cpp
+++ b/src/plugins/VerticalTabs/tabtreeview.cpp
@@ -391,7 +391,7 @@ void TabTreeView::addMenuActions(QMenu *menu, const QModelIndex &index)
     m->addAction(tr("Collapse All"), this, &TabTreeView::collapseAll);
 }
 
-void TabTreeView::reverseTraverse(const QModelIndex &root, std::function<void(const QModelIndex&)> callback) const
+void TabTreeView::reverseTraverse(const QModelIndex &root, const std::function<void(const QModelIndex&)> &callback) const
 {
     if (!root.isValid()) {
         return;
diff --git a/src/plugins/VerticalTabs/tabtreeview.h b/src/plugins/VerticalTabs/tabtreeview.h
index 12db60e15..472f645ad 100644
--- a/src/plugins/VerticalTabs/tabtreeview.h
+++ b/src/plugins/VerticalTabs/tabtreeview.h
@@ -65,7 +65,7 @@ private:
     void initView();
     DelegateButton buttonAt(const QPoint &pos, const QModelIndex &index) const;
     void addMenuActions(QMenu *menu, const QModelIndex &index);
-    void reverseTraverse(const QModelIndex &root, std::function<void(const QModelIndex&)> callback) const;
+    void reverseTraverse(const QModelIndex &root, const std::function<void(const QModelIndex&)> &callback) const;
 
     void closeTree(const QModelIndex &root);
     void unloadTree(const QModelIndex &root);