User Agent: Mozilla/5.0 (Windows NT 6.1; rv:6.0) Gecko/20100101 Firefox/6.0 Build ID: 20110713171652 Steps to reproduce: Closed the Firefox browser. Actual results: I closed the browser, after no longer needing it open, to re-open it a few(10-20) seconds later, when the browser triggered an alert/warning box stating that 'firefox is already open, but may not be responding.' I have only experienced this with Firefox 6 Beta 2, but I haven't tried Beta 1. Expected results: The browser should've re-opened normally. I had to kill the process in task manager to be able to re-open Firefox.
Have you tried with a fresh profile? http://support.mozilla.com/kb/Managing+profiles usually extensions are known to cause this
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