Of the dozen flaws fixed in Firefox 3.0.9, four were rated "critical," two "high," two "moderate" and four "low" in Mozilla's four-step ranking system. It was the most vulnerabilities Mozilla has patched since December 2008, when it quashed 13 bugs.
Other patches prevent from sending users to malicious Web sites and to conduct cross-site forgery request attacks or secretly plant cookie-like objects on a machine to track the user's movements on the Web.
Mozilla addressed several non-security bugs in the update as well, including a database corruption problem that deleted cookies and an issue with on some Web-based services, including AOL's e-mail and instant messaging services.
Tuesday's update, the third this year, follows by four weeks an emergency patch Mozilla hustled out to fix a bug that had in the Pwn2Own hacking contest.