Mozilla's next update for Firefox, slated to ship Tuesday, will check for outdated versions of Flash Player, a frequent target of hackers, the company said on Friday.

The move is the open-source browser maker's opening salvo against out-of-date, open-to-attack plug-ins from vendors like Apple, Adobe, Microsoft and Sun.

One security expert applauded the news.

"This is a great way of improving the security of Web browsers," said Wolfgang Kandek, chief technology officer at security firm Qualys, in a blog entry Saturday.

"Flash is often used by attackers to exploit client machines and unfortunately notoriously difficult to update, requiring, on Windows, different update packages for Internet Explorer and all other browsers."

Firefox 3.5.3 and Firefox 3.0.14, security updates for the newest Firefox 3.5 and 2008's Firefox 3.0, respectively, are set to release Sept. 8. After installing either of those two updates, Firefox users will see a message if their computer has an out-of-date version of Flash Player.

"You should update Adobe Flash right now," the message will read. "Firefox is up to date, but your current version of Flash can cause security and stability issues. Please install the free update as soon as possible."

The message will also include a link to the download site for the latest Flash Player plug-in.

"For now, our focus is on the Adobe Flash Player both because of its popularity and because some studies have shown that as many as 80 per cent of users currently have an out-of-date version," said Johnathan Nightingale of the Firefox security team, in an entry to the group's blog .

Nightingale was referring to a mid-August report by New York City-based security company Trusteer, which said that two weeks after Adobe patched Flash, almost 80 per cent 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 Snow Leopard operating system.

Apple shipped a months'-old copy of Flash with Snow Leopard, and even "downgraded" current versions 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.

Later this month, said Blizzard, Mozilla will publish a page on its Web site that Firefox users can visit to check the update status of other plug-ins.

With the release of Firefox 3.6, now scheduled to ship in early November, the browser will check for newer versions of plug-ins through the same mechanism now used to check for updates to any installed Firefox extensions or add-ons.

"We're going to try to get to the point where you can upgrade [an outdated] plug-in via the plug-in service that we currently use for installations," promised Blizzard.

Mozilla's ambitions are actually grander than that, according to a plans posted on its Web site. Firefox 3.6 will also warn users of any outdated plug-in when they visit a page that requires the use of an older plug-in, when the browser starts up, and when the plug-in list is periodically updated by Mozilla.

The initial goal is to have Firefox 3.6 detect outdated versions of several widely-used plug-ins, including Apple's QuickTime; Adobe's Flash, Shockwave and Reader; Microsoft's Silverlight; and Sun's Java.

Flash is a major target for attackers, who regularly exploit unpatched vulnerabilities in the popular software. Adobe has patched the program twice so far this year, in February and July.

Among the July update patches was a fix for a flaw that hackers had been using for at least a week in widespread attacks.

If Mozilla implements its plug-in plans, Firefox 3.6 will be the first browser to regularly check for outdated third-party add-ons.