This is an interesting development, I noticed the pop-up on my Firefox yesterday. The reason however wasn’t security it was ‘instability’.

It’s a fair move by Mozilla though as the add-on can cause security vulnerabilities in Firefox outside of their control. They can’t fix the software, so the best thing they can do to ensure user safety is to block it.

Compounded with the fact it’s extremely hard for users to remove the add-on themselves the block is a good idea.

Mozilla late Friday blocked the Microsoft-made software that had put Firefox users at risk from attack.

The two-part Microsoft component — an add-on dubbed “.NET Framework Assistant” and a plug-in named “Windows Presentation Foundation” — have been blocked by Mozilla as a precautionary measure, said Mike Shaver, the company’s head of engineering.

“Because of the difficulties some users have had entirely removing the add-on, and because of the severity of the risk it represents if not disabled, we contacted Microsoft today to indicate that we were looking to disable the extension and plug-in for all users via our blocklisting mechanism,” Shaver said in an announcement posted Friday night to the company’s security blog .

The annoying thing is these add-ons are installed in Firefox without any kind of prompt or permission given by the user.

Microsoft pushed them out with the .NET Framework 3.5 Service Pack 1 (SP1) update in February this year, so our browsers have been vulnerable since then.

The software was almost impossible to remove without some registry hacking, Microsoft did remedy this later – but still how many people would know?

Mozilla maintains an add-on/plug-in blocking list that automatically bars risky software from being used by Firefox. The open-source company first used the blocker in 2007. Mozilla has used the tool only nine times, including Friday’s blocking of the Microsoft add-on and plug-in. In May 2008, for example, Mozilla added a Vietnamese language pack for Firefox to the blocking list when the pack was found to contain a worm.

According to Shaver, Microsoft gave Mozilla the go-ahead to block the .Net Framework Assistant and the Windows Presentation Foundation.

Last week, Microsoft’s security team acknowledged that its software — which had been silently installed in Firefox as far back as February 2009 — contained a critical vulnerability that could be used by hackers to hijack Windows PCs. The same vulnerability also affected all versions of Internet Explorer (IE), including the newest version, IE8.

Thankfully Firefox has the blocklist functionality and they have been aggressively moving towards ensuring 3rd party additions are also secure and don’t comprise the integrity of the platform.

Last month they warned users with out of date Flash plugins to update.

Firefox 3.6 will be even more aggressive in this aspect warning users when they visit a site that relies on one or more outdated add-ons.

Source: Network World