Mozilla has patched a pair of nasty flaws in its Firefox browser, two weeks after security researchers first started posting code that showed how they could be exploited in attacks.

The version of Firefox, fixes a pair of related flaws in the URL protocol handler component of Firefox, which is used to launch programs when a user clicks on certain specially crafted web links.

Mozilla rates these problems critical, meaning they are a serious security risk. But they have also proved to be an embarrassment for the open-source project.
Last month, security researcher Thor Larholm showed how to exploit this type of problem in order to make Internet Explorer and Firefox jointly launch software on a user's machine without authorization. To make the attack work, IE would load malformed data from a website, and would then send it to Firefox, which would launch the unauthorised software

Microsoft and Mozilla disagreed about who was to blame, however, with Mozilla initially saying that the attack wouldn't work on Firefox alone.

But last week, Mozilla's security chief Window Snyder admitted that her team was wrong. "We thought this was just a problem with IE. It turns out, it is a problem with Firefox as well," she said in a Mozilla security blog posting. "We should have caught this scenario."

The URL protocol handler flaw will also be patched in Thunderbird, Thunderbird and SeaMonkey 1.1.4, Mozilla said.

The Firefox release also fixes a third security flaw, that Mozilla considers to be less-critical than the URL protocol handler bugs.