User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:2.0b2pre) Gecko/20100630 Minefield/4.0b2pre Build Identifier: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:2.0b2pre) Gecko/20100630 Minefield/4.0b2pre The thanks for using a prerelease page for Firefox 4 doesn't close. It opened after switching to 4 from 3 (not for the first time), and the tab refuses to close, even after moving tabs around, switching tabs, and making new tabs. There were 2 other tabs open before it from opening Firefox (it remembered my tabs from before). I did not have this problem before, and no other tabs are having this problem. Reproducible: Always Steps to Reproduce: Unknown, just trying switching between 3 and 4 and it might happen. Actual Results: Didn't close the tab. Expected Results: Closed the tab.
Which extensions do you have installed? Have you tried running in Safe Mode (http://support.mozilla.com/en-US/kb/Safe Mode)?
Possible duplicate of Bug 610787.
No reply from reporter. So I would say it's a dupe of bug 508738.
I haven't had this problem any more, resolved. (Sorry for the late reply.)