I'm using XP SP3 on my main computer and Vista on my Samsung laptop. My installs both seem to have been OK. I have been loading images on to a couple of sites this morning with no problem and had no problem changing my avatar on here.
Would it be worth while going back to the previous Firefox and then trying a reinstall of this new version?
Add. I have just had a look on mozilla.support.firefox and it appears that there are several people reporting the same problem with crashes as your self but no one seems to have come up with a definitive reason yet.
Seems ironic that this version was supposed to have crash protection as one of it's main new innovations.