Foetz has uploaded a fresh IRIX build of Firefox 1.0.4 which addresses several widely publicized "highly critical" security flaws. It's not clear if these exploits pose a threat under IRIX but it certainly doesn't hurt to be safe.
The updated version can be found in the Nekoware 'current' directory (as of this posting it might still be under 'beta' on the mirrors); related discussion can be found in this thread.
