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}

Is this only about some websites ?

If that is the case, can you give some examples of sites that aren't working ?

Did those websites worked previously, i.e. is this a recent issue ?

• https://support.mozilla.org/en-US/kb/web-pages-dont-load
• https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors

Some websites work fine now, some used to work just fine, but maybe a week or two ago, they stopped. Here's two: www.prescottaz.com http://www.vansairforce.com/community/forumdisplay.php?f=3

These two work fine in safari, just tried 'em. I think there are others but I can't find them now...

Works fine here.

You can try these URLs:

• http://www.prescottaz.com/ => https://www.dcourier.com/
• https://vansairforce.net/community/forumdisplay.php?f=3