When I upgraded to the latest Firefox, I decided to use the full installer. After, I had no access to the internet. After 1/2 hour of checking every thing, I discovered the problem. I do not use a proxy. But something changed that setting.

Press the <Alt> or <F10> key to bring up the tool bar. Followed by;

Windows; Tools > Options Linux; Edit > Preferences Mac; application name > Preferences

Then Advanced > Network. Press the Settings button to the right of Configure How Firefox connects. Check the settings.

Also;

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

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