Steps to reproduce: 1. Click Firefox button 2. Move mouse cursor over the "Web Developer" menu item 3. Wait until the Web Developer menu opens 4. Move mouse cursor over the "Print..." menu item Expected: "Web Developer" menu item should be unhighlighted when "Print..." becomes highlighted What happens: "Web Developer" menu item stays highlighted (until the "Print..." menu opens) Windows XP, latest nightly, 17.0a1 (2012-08-17). Not a regression, also happens in Firefox 4.0

Screenshot: if you follow the steps to reproduce above, this is what happens right after step 4. Only "Print..." should be highlighed. Highlighting more than one menu item at a time is a bug. It doesn't happen anywhere else in the menu.

Animation: added a blue arrow and some red circles to highlight the bug. Note that the bug doesn't appear when hovering over the expansion arrows (as seen on the animation on the right).

This seems to be a <splitmenu> bug. Hovering a <splitmenu> item (e.g. "Print...") after hovering an open <menu> item (e.g. "Web Developer") should remove the <menu> item's _moz-menuactive immediately. The screenshot shows the problem (inspecting chrome://browser/content/browser.xul with Firebug)

The Firefox button is going to be removed in bug 863753.