User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20100101 Firefox/13.0.1 Build ID: 20120614114901 Steps to reproduce: had browser.sessionstore.interval set to default Then I did this to fix the problem: http://www.techmynd.com/firefox-freezes-for-a-moment-after-every-10-sec-fix/ (I haven't restarted FF to see if the changes had any possitive effects, but it's highly plausigle). Actual results: Every 10 sec, FF saves the session, which causes freezes. FF has been on for some days now, and I have multiple tabs open. Expected results: Should not have lagged. I'm not involved in the source code and not really sure what's stored. But wouldn't it be better if the session storing is done on events? That is, the small changes only saved when changes occurs or saved every X seconds IF any changes had been done? Watching an YT-video does not change anything afaik, so I don't see the necessity of the cause of the lag (storing the session). I'm not involved, but if it is what I think it is, it looks somewhat clumsy. :)

Eric, do you still see this?