I've been using it since firefox 1.5. Except for the past six months, I have never witnessed firefox crashing. Now it just crashes all the time.
Funny, im on the latest and Zero crashes
THE BEST METHOD to run PSX games (and everything else for that matter) is via Retroarch - http://buildbot.libretro.com/nightly/
If you have any questions on how to set it up on Windows please feel free to ask, its very easy.