Add a site-specific quirk for Discord

Closes #4379

doc/help/settings.asciidoc

@@ -2693,6 +2693,7 @@ Valid values:
  * +ua-google+
  * +ua-slack+
  * +js-whatsapp-web+
+ * +js-discord+
  * +js-string-replaceall+
  * +js-globalthis+
  * +js-object-fromentries+

qutebrowser/browser/webengine/webenginetab.py

@@ -1152,6 +1152,7 @@ class _WebEngineScripts(QObject):
                 injection_point=QWebEngineScript.DocumentReady,
                 world=QWebEngineScript.ApplicationWorld,
             ),
+            _Quirk('discord'),
             _Quirk(
                 'string_replaceall',
                 predicate=versions.webengine < utils.VersionNumber(5, 15, 3),

qutebrowser/config/configdata.yml

@@ -546,6 +546,7 @@ content.site_specific_quirks.skip:
       - ua-google
       - ua-slack
       - js-whatsapp-web
+      - js-discord
       - js-string-replaceall
       - js-globalthis
       - js-object-fromentries

qutebrowser/javascript/quirks/discord.user.js

@@ -0,0 +1,14 @@
+// ==UserScript==
+// @include https://discord.com/*
+// ==/UserScript==
+
+// Workaround for Discord's silly bot detection (or whatever it is logging
+// people out with vertical tabs).
+
+"use strict";
+
+Object.defineProperty(window, "outerWidth", {
+    get() {
+        return window.innerWidth;
+    },
+});