Help! Firefox is crashing all the time lately. I can't update to a newer version b/c my OS won't support it. Any ideas?

Almost always crashes when I hit home button from Yahoo Mail. Often crashes when in Google Docs, Yahoo Mail, or any of the sites I am working on. I also can't update my OS (Max OSX 10.5.8) This is causing me lots of lost work time... any help would be greatly appreciated.