Mozilla has released an update for Mac OS X users only to fix a couple of crash bugs that may happen when visiting a page with embedded web fonts on Mac OS X 10.7, Lion, or running the latest Java plugin on Mac OS X 10.5.
While Mozilla’s Rapid Release Cycle is so fast (a new release every 6 to 8 weeks), it was thought security or critical stability bugs would come only on major updates. This shows however there’s still room for out of ban releases when critical bugs are to be addressed.
Mac OS X users should update when prompted for it in the next few hours. Note that there are in fact Firefox 5.0.1 downloads available for Windows and Linux, but they are just the exact same build as Firefox 5.0, so you can just pass on it.