Firefox doesn't have any means of doing that, but you could either use your Firewall to block it, or install an add-on like this one: https://addons.mozilla.org/en-US/firefox/addon/foxfilter/ or possibly this one: http://www1.k9webprotection.com/ ---- Incidentally, your Flash player is out of date which exposes your system to exploits. See: http://www.adobe.com/support/security/bulletins/apsb11-12.html Update link at the foot of the page.

There's also this extension. <br /> https://addons.mozilla.org/en-US/firefox/addon/blocksite/

Thank you!