Use :has selector to let toolbars show if appMenu popup is hovered

This requires :has selector support which should be in fx 120

chrome/autohide_bookmarks_and_main_toolbars.css

@@ -65,6 +65,12 @@ See the above repository for updates as well as full license text. */
 /* Selected tab needs higher z-index now to "hide" the broder below it */
 .tabbrowser-tab[selected]{ z-index: 3 !important; }
 
+/* Show when cursor is over main menu popup - this requires :has selector support */
+#mainPopupSet:has(> #appMenu-popup:hover) ~ toolbox > .browser-toolbar{
+  transition-delay: 100ms !important;
+  transform: rotateX(0);
+}
+
 /* SELECT TOOLBAR BEHAVIOR */
 /* Comment out or delete one of these to disable that behavior */
 
@@ -89,13 +95,6 @@ See the above repository for updates as well as full license text. */
   margin-bottom: calc(-1px - var(--uc-bm-height) + var(--uc-navbar-height)) !important;
   z-index: auto !important;
 }
-/* Show when cursor is over popups/context-menus - cannot control which ones */
-/*
-#mainPopupSet:hover ~ toolbox > .browser-toolbar{
-  transition-delay: 100ms !important;
-  transform: rotateX(0);
-}
-*/
 
 /* Uncomment the next part to enable compatibility for multi-row_bookmarks.css
  * This would break buttons placed in the toolbar,

chrome/autohide_toolbox.css

@@ -36,15 +36,18 @@ See the above repository for updates as well as full license text. */
   pointer-events: none;
 }
 
-
-/* #mainPopupSet:hover ~ toolbox, */
-/* Uncomment the above line to make toolbar visible if some popup is hovered */
 #navigator-toolbox:hover,
 #navigator-toolbox:focus-within{
   transition-delay: 33ms !important;
   transform: rotateX(0);
   opacity: 1;
 }
+/* This ruleset is separate, because not having :has support breaks other selectors as well */
+#mainPopupSet:has(> #appMenu-popup:hover) ~ toolbox{
+  transition-delay: 33ms !important;
+  transform: rotateX(0);
+  opacity: 1;
+}
 
 #navigator-toolbox > *{ line-height: normal; pointer-events: auto }