The new "Updates" feature of Firefox 1.0 (and the old idea of system-wide plugins) require you to run Firefox as root.
I suggest that we follow a similar philosophy to the "games" to allow more access. Have a "mozilla" group who owns /usr/lib/MozillaFirefox (and /usr/lib/MozillaThunderbird) with write access. Then any user added to the "mozilla" group can update firefox and/or thunderbird, and add system-wide plugins.
No, the sysadmin can handle firefox updates, there's no reason to give users access. Users aren't allowed to update games either, only the score files.