I was able to get passed this failure by uninstalling firefox - updating my system (new kernel) and then re-installing the firefox package. Not sure if others have done this as well???
FYI - 2.6.15-23-386 -- upgrade to firefox 1.5.dfsg+1.5.0.3-0ubuntu2 fails https://launchpad.net/bugs/44487 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
