Firefox and Opera stop working the firewall not let it out allso may stop activation & the fix, http://support.mozilla.com/en-US/kb/Cannot+connect+after+upgrading+Firefox
Cannot connect after upgrading Firefox
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This article covers why you would not be able to access any web sites
The most common cause of this problem is firewall software. Some firewalls silently block the updated version of Firefox from accessing to the Internet. Even if the firewall is supposedly disabled or uninstalled, it may still be active.
Click on the tutorial for the firewall you are using.