User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; cs; rv:1.9b5) Gecko/2008032620 Firefox/3.0b5 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; cs; rv:1.9b5) Gecko/2008032620 Firefox/3.0b5 When firefox 3 beta x is not running and i click to some URL in thunderbird, firefox will hang and must be terminated in task manager and started separately, than i choose profile, and firefox is runing correctly Reproducible: Always Steps to Reproduce: 1.run firefox 2.run other apps that can use browser 3.

this bug is only in Firefox3

I have experienced this as well. This happens when there are two or more profiles in the Profile Manager, the check box "Don't ask at startup" it unchecked, and I click on a URL in an email application (Outlook in my case) or URL shortcut on the desktop when Firefox is not running. To open URLs from other programs, Firefox must first be started using the program shortcut and a profile selected in the Profile Manager.

Same problem has been reported to Bugzilla Japan, and I could observe same phenomenon with Firefox Trunk(6/03 build) on MS Win-XP SP2. When all of next conditions met, I could see the problem. 1. "Default Browser" on MS Win is set as Firefox 3 2. Multiple profiles of Firefox exist 3. "Don't ask at start up" is not checked in profile manager panel 4. No active Firefox exists 5. "Default Browser"(Firefox 3 in this case) is invoked via DDE (Outlook, URL short cut, etc. probably uses DDE) As Mikael Pettersson says, when condition of 3 is changed to false, i.e. "Don't ask at start up" is checked, Firefox 3 started using last used profile. When hang of newly started firefox.exe, Virtual Memory Size of it was around 10 KB. This is almost same as VM size while profile manager panel is displayed. It looks to be hang in Profile Manager. Confirming.

It seems to be not-so-new problem. Probably DUP of Bug 395891 which opened on 2007/9/12.