Mozilla is rolling out an update of its Firefox Web browser that adds support for plugin isolation. Version 3.6.4, which includes the new feature, was officially released on Tuesday and will be deployed soon through the browser's automated update system.

It is unusual for Mozilla to deploy a major new feature in a minor point update, but the plugin isolation capability is a worthy exception to the rule, since it will significantly improve the browser's stability. In the new version of Firefox, plugin components like Flash and Silverlight will run in external processes. When these plugins crash, the browser itself will not be terminated.

Browser vendors are increasingly adopting the multiprocess approach in order to improve stability and security. In some browsers, such as Chrome and Internet Explorer, the tabs themselves are sandboxed into separate processes. Mozilla launched a project last year called Electrolysis with the aim of bringing experimental multiprocess browsing to Firefox. Isolating plugin runtimes in separate processes is Firefox's first step towards full multiprocess browsing.

The plugin isolation feature by itself has significant value for end users, which is why Mozilla is rolling it out as an addition to the current stable 3.6 series.

"Results from our 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's Mike Beltzner wrote in the official Mozilla blog. "When a plugin crashes or freezes while using Firefox, users can enjoy uninterrupted browsing by simply refreshing the page."

We tested the feature several months ago when it was previewed in early experimental builds. When the Flash plugin crashes, the Flash content in webpages is replaced with an error message informing the user of the crash. The browser itself will survive and continue running.

For more details about Firefox's plugin isolation, you can refer to the Crash Protection FAQ at the Mozilla wiki. You can find a download link and more details about version 3.6.4 in the official release notes.