[PLUG] Firefox or security problems

[John Jason Jordan]

Last Sunday at the Clinic I did a dist-update on my Xubuntu 16.04 - an
update, not an upgrade to 18.04. After rebooting everything works
perfectly, except Firefox. The update installed a new version of Firefox
so I now have Firefox Quantum 68.02 64-bit, 'Mozilla Firefox for Ubuntu
canonical 1.0.' I recall seeing some security updates flash by during
the update also, but I didn't take note of exactly what they were.

Either Firefox or the security updates has made Firefox unusable. It
launches and appears to run fine, but no web pages can find the
internet.

After hours of poking at things I discovered a solution - launch
Firefox in Safe Mode. In Safe Mode all web pages find the internet and
function as before. Unfortunately, Safe Mode disables all extensions
and add-ons. They are still installed and I can see the list, but all
are marked 'disabled.' Now, logically, I should just re-enable them one
at a time, until I find the culprit. But in their wisdom, while in Safe
Mode, Mozilla made it impossible to re-enable any add-ons, or even add a
new one.

Thinking I was being very clever I closed Firefox and re-launched it in
normal mode. As before, no web page could find the internet. Then I
went into the list of extensions and manually disabled each one, then
shut down and re-started Firefox. All my add-ons remained disabled, but
web pages still could not find the internet.

I scoured the Ubuntu forums, but apparently I am the only one in the
history of Ubuntu that this has happened to. Ditto for all the Help
pages and forums at Mozilla.

I have also poked at the security settings in Firefox, including making
them match Chromium (as best I could), but so far no luck. Chromium, of
course, continues to function normally, and in spite of the fact that
the dist-update also included a new version of Chromium.

I'm out of ideas. :(  Suggestions welcome!