This seems like a problem with cached DNS entries and may not be related to Firefox. Please try the following: #In Windows, press Start, then "Run..." (alternatively, hold down the Win key on your keyboard and press R) #type "ipconfig /flushdns" without the quotes and press Enter #In Firefox, navigate to www.facebook.com and if it still doesn't work, click reload (or press the F5 key on your keyboard). Unrelated to your issue, it looks like you're using a very old version of Firefox. You should upgrade to the latest version, 9.0 -- just go to the Help menu and click Check for Updates. This link walks you through the process: https://support.mozilla.com/en-US/kb/Updating%20Firefox?s=updating+firefox&r=0&as=s#w_how-do-i-manually-check-for-updates