"One of the security fixes in Firefox 3.0.9 introduced a regression that caused some users to experience frequent crashes," said Mozilla officials.
An investigation of those crashes revealed evidence of memory corruption that could possibly be used to execute remote code.
The release notes also mention "a major stability issue", but that appears to be a reference to the same underlying problem.
Online discussions among developers working on the issue suggest that the issue arose from a bug fix that did not take into account another change that had been made.
The 3.0.10 update can be applied to an existing Firefox installation by using the Check for Updates command, or the entire program can be downloaded via Mozilla's site.
Versions are available in a variety of languages for Windows, Mac OS X and Linux.
A Welsh version of Firefox is currently in beta test.