hello Barnetta, normally such issues are caused by a firewall/security software which doesn't recognize & therefore blocks new firefox versions. please remove all program rules for firefox from your firewall and let it detect the new version of the browser again.

Fix problems connecting to websites after updating Firefox

Barnetta said

Unable to Connect message appears for every website. IE works fine. I believe the problem has something to do with the Firefox update notification I got this morning. I uninstalled/reinstalled Firefox and the problem persists. I tried the restart without add-ons, still doesn't work. What's next?

Well I think the firefox update messed with my security program and things needed to be uninstalled/reinstalled. It might be a good idea for new Firefox updates not to be so troublesome for the user. Not everyone is interested or skilled in fiddling with programs etc. tiresome.