Mozilla has just released an updated version of its popular open source browser software to address a security vulnerability that had become the target of several attacks in recent days. Firefox 3.5.1 patches a critical flaw in the new TraceMonkey JavaScript engine’s just-in-time (JIT) compiler, which was discovered last week and publicly disclosed just three days ago.

Exploit code for the vulnerability was posted online this past Tuesday, so kudos to Mozilla for acting swiftly on what might otherwise have been a potentially nasty problem – enabling attackers to install malware on vulnerable machines. This update also appears to fix a number of other stability and security issues. Users who have turned off automatic updates can use the “Check for Updates...” feature under Help or choose the appropriate OS below to download.

If you followed our advice on how to avoid infection and disabled the JIT compiler, you might want to revert things to speed up your browser’s JavaScript performance. Just enter “about:config” in the address bar and double-click the line containing “javascript.options.jit.content”, which should change the value to “true”.

Download: Firefox 3.5.1 for Windows | Mac OS X | Other systems and languages