If you have this problem you know how frustrating it can be. Every time you start Firefox it wants to start in offline mode. To get around this you have to go to the File menu and uncheck the Work Offline box. And all your open tabs takes a lot of time to load :(

open the about:config window (you will most likely have to click the check box promising you’ll be careful using this configuration page), and do a search for the string:

toolkit.networkmanager

This string should have a true value