Mozilla has released updates to its Firefox browser and Thunderbird email client that fix a number of critical security flaws in the open-source products.

The Firefox update addresses 12 security flaws. The release also includes some fixes designed to make the browser more stable, Mozilla said.

Five of the browser flaws are serious enough that an attacker could possibly use them to run unauthorised software on an unpatched system, Mozilla confirmed. Security vendor Secunia rates this update as "highly critical," its second-highest rating of importance.

There are a couple of mitigating factors, however. First, hackers must still develop code that takes advantage of these flaws before users can be attacked. Second, a user would need to be tricked into visiting a malicious website for the attack to occur.

Eight bugs have been fixed in Thunderbird, one of which is considered critical by Mozilla.