Sometimes, for about an hour/two hour block, Firefox (and Thunderbird) while crash within a few seconds of starting up. This includes starting in safe mode, and often before I can attempt to restore or start new session. Often it will work fine, but sometimes I will click a link or attempt to go back a page and the pinwheel will come up for a couple minutes then it crashes, and will do so for the next couple hours. I've re-downloaded Firefox, it still happens. Only Plug-in that's out of date is Silverlight, the rest are either up to date or unknown. What can I do?