This sucks !

Same here its so anoyying i had to move to opera for now

This may be a problem with the Silverlight plugin. See Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

It started as soon as the latest version of Firefox was installed.

I disabled the MSN toolbar plugin and the problem went away

I disabled the MSN toolbar plugin and the problem went away Yep fixed mine.

This message is from an add-on, the MSN or Bing Toolbar.

Disable this add-on in Tools -> Add-ons or uninstall it from Start -> Control Panel -> Programs and Features.