RC1 is stable its been available since May and they package it in rawhide for F10. My windows machine has been running it without a hitch unlike beta 5
At least they should be packaging them in updates-testing so you can add them if you want to or not.
I already tried to rpmbuild RC2 as well as RC1 and it fails on it can't find firefox-2.0 in usr/lib as since they insisted on using beta5 and its in /usr/lib as firefox-2.0b5.
My opinion is they have 'over taxed' themselves with 4 releases going right now. F7, F8, F9 and rawhide (F10). It would have been sensible to hold off on F10 until F7 was EOL. If they want to have everything going then try to do a better job answering bugzilla's. The fedora forum is full of firefox 3 issues with B5.