Mozilla has released a new update for the current Firefox 3.0.x branch. As usual, it provides a handful of stability fixes and patches for nine security bugs including one labeled as critical that could lead to arbitrary code execution.
To get the update, select Check for Updates… in the Help menu and follow the onscreen instructions.
Note that the critical bug fixed in this release is also present in the latest Firefox 2.0.x branch (unsupported since last December), so a bug fix will not be made available. Firefox 2.0.x users should seriously consider moving to Firefox 3 as soon as possible.