I seem to recall that I have to reinstall my SpellCheck add-on in Firefox if ever I upgrade FF.
And IE9 of course is a Beta, so possibly any spell check extension has not caught up with this new version yet.
I think IE 9 beta is pretty good. But I realized today that it is still missing a spellchecker that I think all other browsers have. This was one thing I grew tired of with IE8.
What else is missing from IE9 that you that would be there.