Mozilla just released Firefox 3.5.6, and while the fix list isn't that long, the one to pay attention to that was repaired is:

Crashes with evidence of memory corruption

FF 3.5.5 for whatever reason just blew up in memory use, and so far since upgrading to 3.5.6, that rapid overuse of memory seems to have decreased quite a bit.

This upgrade did not break any of my FF add-ons either, so good deal there. Chances are very good nothing will happen to yours either, should you use them.

This is a recommended download, so go get it. You can do this from Help/Check for Updates in Firefox itself, or just go to the web site to download.