Add workaround for missing per-domain setting changes

Fixes #4920

doc/changelog.asciidoc

@@ -56,6 +56,8 @@ Fixed
 - When quitting qutebrowser, components are now cleaned up differently. This
   should fix certain (rare) segmentation faults and exceptions when quitting,
   especially with the new exit scheme introduced in in PyQt5 5.13.1.
+- Added a workaround for per-domain settings (e.g. a JavaScript whitelist) not
+  being applied in some scenarios with Qt 5.13 and above.
 
 v1.9.0 (2020-01-08)
 -------------------

qutebrowser/browser/webengine/webenginetab.py

@@ -1490,6 +1490,21 @@ class WebEngineTab(browsertab.AbstractTab):
         except browsertab.WebTabError as e:
             message.error(str(e))
 
+    @pyqtSlot(QUrl)
+    def _on_url_changed(self, url: QUrl) -> None:
+        """Update settings for the current URL.
+
+        Normally this is done below in _on_navigation_request, but we also need
+        to do it here as WORKAROUND for
+        https://bugreports.qt.io/browse/QTBUG-77137
+
+        Since update_for_url() is idempotent, it doesn't matter much if we end
+        up doing it twice.
+        """
+        super()._on_url_changed(url)
+        if url.isValid() and qtutils.version_check('5.13'):
+            self.settings.update_for_url(url)
+
     @pyqtSlot(usertypes.NavigationRequest)
     def _on_navigation_request(self, navigation):
         super()._on_navigation_request(navigation)