The project expands on an initiative launched last month to encourage Firefox users to update old versions of Adobe Flash. According to Mozilla, more than 10 million people have clicked through from their warning page to Adobe’s update site since then -- which is five times the click through their "What's New" page typically sees.
Rather than warning users only when a newer version of Firefox is installed, Mozilla plans to include built-in support for this plugin checking functionality starting with the browser's next release. This means that when visiting a page with Firefox 3.6, users will be notified if any if the plugins used by the site has been updated. Presumably, an option to manually check for updates will also be available -- just like with extensions.
Initiatives like these really show Mozilla's dedication to the security of web users, even more so as they apparently want to make the service compatible with other browsers as well. I ran the plugin check and actually found a few of them were out of date. Did it uncover any surprises for you?