I have Firefox 7 and it hangs or freezes about every 10 minutes with all addons disabled. It was driving me nuts! I finally found a solution reading this blog entry and I downloaded the add-on Places Maintenance. I launched the add-on and chose Expire and Execute and after a minute or so my Firefox has been free from this hanging issue (for 2 days now!). It’s an excellent solution but it might not work for everybody.