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}

Firewall has been configured. It was one of the first things that I checked.

Re-read my post.

Your suggestion did not seem to work. Thanks for the suggestion, though.

Start Firefox in Safe Mode {web link}

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

I appreciate you taking the time to help with this, btw. Yes, still unable to connect even in Firefox safe mode. I made sure my AV (Eset NOD32) was paused, as well.

What's your computer system and Firefox version?

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select Network.

[v56+] Type about:preferences#general<enter> in the address bar. Look for Network. +++++++++++++++++++++ Look for Configure How Firefox Connects and press the Settings button. If you are using a proxy, make sure those settings are correct. If there is no proxy, first try No Proxy. If there is a problem, then try System Proxy.