Mozilla has patched eight flaws, including five critical vulnerabilities in versions 3.5 and 3.6 of the Firefox browser.
The critical rating by Mozilla indicates that attackers could exploit these flaws to run code and install software, requiring no user interaction beyond normal browsing.
Three flaws were rated "moderate", which indicates vulnerabilities that would otherwise be "critical" except they only work in uncommon non-default configurations or require the user to perform complicated or unlikely steps.
Mozilla has also announced the addition of crash protection to Firefox 3.6.4 aimed at keeping the browser running even when a plug-in application fails.
Results from beta testing show Firefox 3.6.4 will significantly reduce the number of Firefox crashes experienced by users who are watching online videos or playing games, Mozilla said.
"When a plug-in crashes or freezes while using Firefox, users can enjoy uninterrupted browsing by simply refreshing the page," said Mozilla's Christian Legnitto in a blog post.
"At this time, Firefox offers crash protection for Adobe Flash, Apple Quicktime and Microsoft Silverlight on Windows and Linux computers," he wrote.
Support for other plug-ins and operating systems will become available in a future Firefox release.
Firefox users are encouraged to upgrade for free by using the "Check for Updates" function in the Help menu, or by visiting the Firefox website, Mozilla said.