This is with: firefox-1.1-0.2.2.deerpark.alpha2 If I hit a page that needs a plugin I don't have or say an MP3 file which I don't currently have an plugin for Firefox crashes immediately. Totally repeatable for me.
I think this is a dupe of bug 163653. Try firefox-1.1-0.2.3.deerpark.alpha2 when it hits rawhide tomorrow.
*** This bug has been marked as a duplicate of 163653 ***