In trying to help out with SUMO Day, came across a user who was having a startup hang problem. They suspect a specific URL of causing problems, but I cannot reproduce it locally. The URL on sumo is: https://support.mozilla.com/en-US/questions/901060 And the suspect URL is http://brennadaugherty.tumblr.com/ It does lots of fun stuff like changing the window title and cursor, so there may be something to it.
I'd push back there and see if there's anything else. The person wasn't sure it was that url and they said they didn't have a sessionstore.js file... There's something going on and while I'm not ruling out a problem here, it sounds like something specific to that user.
Verified as WFM on: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:12.0a1) Gecko/20120109 Firefox/12.0a1 This seems to be an issue specific to that user, as Paul said above. Unless anyone else can reproduce this issue and give more details about it, the bug will be closed as RESOLVED INCOMPLETE.