Critical JavaScript flaw hits Firefox 3.5

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A newly-discovered critical flaw in Firefox 3.5's JavaScript compiler could be used to execute malicious code, Mozilla developers have admitted.

According to the Mozilla security blog, the vulnerability in the Just-in-time JavaScript compiler was discovered last week - just over a week after Firefox 3.5 was made available for download. The TraceMonkey JavaScript engine has been patched once already.

"Mozilla developers are working on a fix for this issue and a Firefox security update will be sent out as soon as the fix is completed and tested," Mozilla noted on its security blog.

In the mean time, users should either run Firefox in Safe Mode or disable the compiler. Mozilla gave instructions on how to do that here, but acknowledged it would hurt JavaScript performance. The flaw can only be exploited if a Firefox user visits a web page containing malicious code.

Click here for our review of Firefox 3.5 - and here to learn more about the browser.