facebook + flash are a lethal combination, sometimes. If you are running flash based games on facebook or flash based anything, that can have the effect that was described.

I've seen that same effect with firefox. When it gets into that mode where it's doing nothing but eating all the cpu cycles, you just have to kill it (sometimes in taskmgr) and restart it. Frankly, I don't think IE is any better either. It's the flash based stuff (not flash-based video) that seems to push it over the edge. Though I admit, it's hard to pinpoint what exactly is going on at that point, since I might have 10 or more tabs open, many of them with active content (google reader, calendar, etc.)

One thing you can do with the latest version of ff is the plugin version check. (from tools/add-ons/plugins/find updates). Note, this is different from the "extensions" check, which has been around forever.

-David