I got the same thing, it is just some update that makes it unreliable or something. Should be fixed soonish.
People objected to the .NET plugin for Firefox that Microsoft force-installed via Windows Update. It WAS unstable and broke stuff, so Mozilla blocked it in their latest update. Linux = no problems like this.
Bad news: Mozilla has now decided* these plugins are no longer a threat, and has begun the process of de-blacklisting them. *Decided = threatened/bribed by certain residents of Washington state?