Is your whole network down, or just Firefox? Are there any error messages? Contact your provider and have them test your service. Also, unplug your modem. Wait about 30 seconds before plugging it in. * Some problems occurs when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again; * Make sure your Internet security software is up-to-date (i.e. you are running the latest version) * Remove Firefox from your program's list of trusted or recognized programs, then add it back. For detailed instructions, see '''[https://support.mozilla.org/en-US/kb/configure-firewalls-so-firefox-can-access-internet?esab=a&s=Configure+firewalls+&r=0&as=s Configure firewalls so that Firefox can access the Internet.]''' {web link}

Did you try to boot Windows in Safe Mode? Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test. *http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/