Disable this plug in for sure.
"The reason is that .NET Framework 3.5 SP1 installs a 'Windows Presentation Foundation' plug-in in Firefox."
http://www.computerworld.com/s/artic..._users_at_risk
This is an easier read for me.
http://blogs.techrepublic.com.com/security/?p=2522
Add on block list
http://www.mozilla.com/en-US/blocklist/
http://i.imgur.com/8pct5.png