Try to avoid really hiding menus b=127244 r=gavin a=mconnor

toolkit/content/widgets/toolbar.xml

@@ -267,6 +267,11 @@
   </binding>
 
   <binding id="menubar" extends="chrome://global/content/bindings/toolbar.xml#toolbar-base" display="xul:menubar">
+    <content height="0">
+      <xul:hbox flex="1">
+        <children/>
+      </xul:hbox>
+    </content>
     <implementation implements="nsIAccessibleProvider">
       <property name="accessibleType" readonly="true">
         <getter>

toolkit/content/xul.css

@@ -33,7 +33,6 @@
    :: kinds of windows (not JUST browser windows) with toolbars
    ::::: */
 
-window[chromehidden~="menubar"] .chromeclass-menubar,
 window[chromehidden~="directories"] .chromeclass-directories,
 window[chromehidden~="status"] .chromeclass-status,
 window[chromehidden~="extrachrome"] .chromeclass-extrachrome,
@@ -255,6 +254,17 @@ toolbarpaletteitem[place="palette"] {
 
 menubar {
   -moz-binding: url("chrome://global/content/bindings/toolbar.xml#menubar");
+  -moz-box-orient: vertical;
+  -moz-box-pack: end;
+}
+
+window[chromehidden~="menubar"] .chromeclass-menubar,
+menubar[hidden="true"],
+menubar[_moz_collapsed="true"],
+menubar[collapsed="true"] {
+  min-height: 0%;
+  display: -moz-box;
+  visibility: visible;
 }
 
 /********* menu ***********/