Nightingale was referring to a mid-August report by New York City-based security company Trusteer, which said that two weeks after , almost 80% of the 2.5 million PCs scanned by Trusteer's security service had not yet been updated.

Some of the users most immediately affected by Firefox's new plug-in check will be those running Apple's new operating system. Apple shipped a months'-old copy of Flash with Snow Leopard, and even during the upgrade to a vulnerable edition of Flash.

Starting Tuesday, Firefox users running Snow Leopard will be alerted to that fact after they update their browsers.

Mozilla plans to expand the plug-in check, Nightingale added. "Mozilla will work with other plug-in vendors to provide similar checks for their products in the future," he said. "Keeping your software up to date remains one of the best things you can do to keep yourself safe online, and Mozilla will continue to look for ways to make that process as easy as possible for its users."

In a follow-up comment to Nightingale's post, Christopher Blizzard, a Mozilla evangelist and former member of the Mozilla Foundation's board, spelled out in greater detail just what Mozilla wants to do.