When Firefox is running normally, you can use its built-in Task Manager by pressing Shift+Esc or by copy/pasting '''about:processes''' to the address bar and pressing Enter to load that page. I think by the time Firefox freezes, it would be too late. The point is just to see whether any particular process is using a lot of CPU or growing its memory by leaps and bounds to try to figure out whether this is coming from a site you're using, or add-ons, etc. And also to notice the pattern that there are three or four processes Firefox always runs for itself, and then there are site-specific processes used for isolation (for stability and data security).