If you are encountering numerous problems with Firefox not connecting to various sites, it's most likely that you have Zone Alarm<ZA> Firewall installed. What you need to do is remove Firefox from the Acceptable Programs List within Zone Alarm, close ZA, then reopen Firefox and let ZA prompt you to Allow or Deny it access to the Internet. Click "Always Allow" and that should resolve the issue. If you're still having problems, I suggest a support ticket (email) to Mozilla and/or a Google Search of the problem as you may have other issues such as 2 versions of Firefox installed, etc.
