User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:18.0) Gecko/20100101 Firefox/18.0 Build ID: 20130104151948 Steps to reproduce: When I hold the mouse over a menu item on http://www.betathetapi.org the child menu items don't expand properly. This problem is specific to Firefox v 18.0. The site renders perfectly on all other browsers and older versions of Firefox. Actual results: All of the child menu items seem to stack on top of each other. Expected results: The parent menu should have created a drop down menu with all of the child menu items contained within it.

I can't reproduce this with Firefox 18 on Windows7 and OSX10.8 Can you please try it in the Firefox safemode ? http://support.mozilla.org/en-US/kb/Safe+Mode Is this report about OSX or Windows8 ?

Works for me with 2013-01-15-03-09-36-mozilla-central-firefox-21.0a1.en-US.linux-x86_64. Are you using a single monitor?

I tried to access the site in safe mode, but no dice. The issue was replicated on OS X, Windows 7 and Windows 8. I am using a single monitor.

I can now reproduce this, strange Last good nightly: 2012-08-04 First bad nightly: 2012-08-05 Pushlog: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=20fc34efd733&tochange=9453cf029b72 Could be again the checkins from Matt Woodrow, bisecting now.

The site uses: MooTools={version:"1.2.5" This version is known to be broken in Firefox18, please read bug 789036 This is your page, right ?

Reopening for tracking purposes.

This has been fixed And marking as invalid as per matti comments