Firefox 2.0.0.20 added the patch Mozilla said had been due to a "clerical error." The patch, which , the director of Firefox, had said was among the less severe of the 10 described Tuesday, plugged a hole that could have been used by attackers to from users.

Although only the Windows version of Firefox 2.0.0.19 lacked the patch, the and Linux versions were also re-issued as 2.0.0.20 to keep all platforms in sync.

Mozilla took the opportunity to urge users one more time to upgrade to the newer Firefox 3.0, as it has now officially retired the older browser, and will not issue any additional security fixes.

Since it rolled out Firefox 3.0 last June it has twice to Firefox 2.0 users, most recently just two weeks ago. It plans to make one final offer early next month.

Users can from Mozilla's Web site, retrieve it via Firefox's built-in update tool, or simply wait for the automatic update notification to appear.