writes "Around 11:45 PM Friday night, I was prompted by Firefox that it had disabled the addons that Microsoft has been including with .NET — specifically, the .NET Framework Assistant and the Windows Presentation Foundation. The popup announcing this said that the 'following addons have been known to cause stability or security issues with Firefox.' Thanks, Mozilla team, for hitting the kill switch and hopefully this will get Microsoft to release a patch sooner."
Here's the Mozilla security blog entry
announcing the block, which Mozilla implemented via its blocklisting mechanism