I can't get Firefox to open any web site after Mac os Update Golden Gate

Were you able to access this support site using the same browser (so it's not "any web site" but just a specific set perhaps?) or you had to use a different device to post this question?

There are some DNS/HTTP3 wrinkles on Golden Gate and updates should be shipping remotely, do you have "remote improvements" enabled there?

I sort of have a similar issue. However, I can visit websites, but every site is slow and laggy after installing Golden Gate this morning. Never any issue before installing Golden Gate. Other browsers are working fine as well. I have performed a refresh, ran troubleshooting mode, shut off extensions, cleared cache, etc. Nothing has worked.

I still can't find a solution and can't access websites. I can only access websites if I log in in troubleshoot mode, which I suspect isn't completely safe. I tried almost everything as braden2 did and didn't see any improvement either. For now, I managed to export all my Bookmarks to Chrome and set it as my default browser, since that is the only way to keep working. I hope this isn't the demise of Firefox.

I can only access websites if I log in in troubleshoot mode, which I suspect isn't completely safe.

It is completely safe. And in your case most likely points at an extension. The guide at Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems has the steps to eliminate what's in the main profile that's not working.

This could be confirmed by quickly creating a new profile (e.g. from the Profiles menu) and starting up this clean slate to check if that one can connect.