autohide_bookmarks_toolbar: add workaround for fx 119 with default theme

In 119 the light-dark() computation doesn't always resolve correctly and
when default theme is used --toolbar-bgcolor ends up using it.
See bug 1853524 for some more info.
This fixes #315

chrome/autohide_bookmarks_toolbar.css

@@ -28,7 +28,16 @@ See the above repository for updates as well as full license text. */
   background-position-y:top,top,var(--uc-bg-y),var(--uc-bg-y),var(--uc-bg-y);
   background-image: var(--toolbar-bgimage,linear-gradient(transparent,transparent)), linear-gradient(var(--toolbar-bgcolor),var(--toolbar-bgcolor)),var(--lwt-header-image,var(--lwt-additional-images)) !important;
 }
-
+/* This is a workaround for fx 119 specifically for users that use default theme, should remove when 120 is released. See bug 1853524 */
+#PersonalToolbar:not(:-moz-lwtheme){
+  --toolbar-bgcolor: #f9f9fb;
+}
+/* ...and for dark variant */
+@media (prefers-color-scheme: dark){
+  #PersonalToolbar:not(:-moz-lwtheme){
+    --toolbar-bgcolor: rgb(43, 42, 51);
+  }
+}
 #PlacesToolbarItems > .bookmark-item,
 #OtherBookmarks,
 #PersonalToolbar > #import-button{