toggle tabs toolbar with alt: Make Alt only show tabs toolbar

This is pretty much complete rewrite, Alt now only show tabs toolbar,
but when you press Alt again while also hovering tabs toolbar, then
menubar items will be shown and window controls likewise.

There's a weird behavior, some 1px slice that hides tabs toolbar when
cursor is moved from tabs to window controls, but doesn't trigger from
other direction mysteriously. But window controls can be accessed when
cursor is already where window controls would appear when Alt is pressed
the second time.

chrome/toggle_tabs_toolbar_with_alt.css

@@ -1,18 +1,30 @@
 /* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/toggle_tabs_toolbar_with_alt.css made available under Mozilla Public License v. 2.0
 See the above repository for updates as well as full license text. */
 
-/* Show tabs toolbar with Alt-key. Menubar must be disabled for this to work */
+/* Show tabs toolbar with Alt-key. Menubar must be disabled for this to work.
+ * To show window controls and/or menubar hit Alt again while cursor is over tabs toolbar */
 
-#titlebar { -moz-appearance: none !important }
+:where(#titlebar:not(:hover) > #toolbar-menubar[autohide="true"][inactive]) + #TabsToolbar {
-:root[tabsintitlebar][sizemode="maximized"]{ padding-top: 8px !important; }
+  visibility: collapse;
-#titlebar:not(:hover) > #toolbar-menubar[autohide="true"][inactive] + #TabsToolbar { visibility: collapse }
+}
-
-/* Behavior 1 - Alt-key toggles menubar as normal */
-#titlebar:hover > #toolbar-menubar[autohide="true"]{ height: calc(var(--tab-min-height) + var(--space-above-tabbar) - var(--tabs-navbar-shadow-size)) !important; }
-
-/* Behavior 2 - Alt-key only shows tabs toolbar */
-/* To show window controls, hit Alt again while cursor is over tabs toolbar */
-/*
 #toolbar-menubar[autohide]:not([inactive]),
-#toolbar-menubar[autohide="true"]:not([inactive]) + #TabsToolbar > .titlebar-buttonbox-container{ visibility: collapse !important }
+#toolbar-menubar[autohide="true"]:not([inactive],:hover) + #TabsToolbar > .titlebar-buttonbox-container{
-*/
+  visibility: collapse !important;
+}
+#menubar-items:has([_moz-menuactive][open="true"]),
+#toolbar-menubar[autohide]:hover > #menubar-items,
+:root:not([sizemode="fullscreen"]) #titlebar:hover #toolbar-menubar[autohide][inactive] > #menubar-items{
+  visibility: visible;
+  position: absolute;
+  z-index: 1;
+  height: calc(var(--tab-min-height) + 2 * var(--tab-block-margin));
+  background-color: -moz-dialog;
+  align-items: stretch;
+}
+#main-window[sizemode="fullscreen"] #TabsToolbar{
+  visibility: visible !important;
+}
+#main-window[sizemode="fullscreen"] #toolbar-menubar > #menubar-items{
+  visibility: collapse;
+}
+#main-menubar{ height: 100%; }