Are you able to access the web, or is some of it blocked?

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Some problems occur 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. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

Thanks FredMcD for your recommendation. However, what I did was I tried to go back to before the last automatic security system update by Microsoft. After it went through all the motion but it failed to revert. it said so on the screen. I shut down the computer, restarted it. Tested Firefox and it worked. I won't even try to analyze what had happened. Merry Christmas to all.

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.

Sometimes, after a major update, the computer needs to be rebooted.