Merge remote-tracking branch 'origin/develop' into develop

src/vector/index.js

@@ -313,7 +313,11 @@ async function loadApp() {
         if (match) {
             if (match[1] === theme) {
                 // remove the disabled flag off the stylesheet
-                a.removeAttribute("disabled");
+
+                // Firefox requires setting the attribute to false, so do
+                // that instead of removing it. Related:
+                // https://bugzilla.mozilla.org/show_bug.cgi?id=1281135
+                a.disabled = false;
 
                 // in case the Tinter.tint() in MatrixChat fires before the
                 // CSS has actually loaded (which in practice happens)...
@@ -324,6 +328,11 @@ async function loadApp() {
                 a.onload = () => {
                     Tinter.setTheme(theme);
                 };
+            } else {
+                // Firefox requires this to not be done via `setAttribute`
+                // or via HTML.
+                // https://bugzilla.mozilla.org/show_bug.cgi?id=1281135
+                a.disabled = true;
             }
         }
     }