Firefox exists and runs on the system. Firefox is the default and I believe the issue is Firefox as it is slowing system resources graphically and I caught it performing an update without me performing a "software update"
I have open a case with mozilla as this is not Ubuntu issue sinc no other browser is running.
@bunnion, is that firefox from default install or at any time you manually installed it? If so, was it a snap package or downloaded it straight from firefox site? May be you can share screenshot of 'About Firefox' window? Or the output of following.
dpkg -l | grep firefox
snap list | grep firefox
I'm asking because, I see firefox snap version is 82.0.3 whereas deb package is 83. Following is status on my PC.
(base) sai@hirsute:~$ dpkg -l | grep firefox
ii firefox 83.0+build2-0ubuntu1 amd64 Safe and easy web browser from Mozilla
ii firefox-locale-en 83.0+build2-0ubuntu1 amd64 English language pack for Firefox
(base) sai@hirsute:~$ snap list | grep firefox
(base) sai@hirsute:~$ snap search firefox
Name Version Publisher Notes Summary
firefox 82.0.3-1 mozilla* - Mozilla Firefox web browser
If so, unless you want non system-provided pacakge, remove the other instance and install from official repo and see if it fixes the issue.
If that is not the case, you could try two things.
See if there are still browser folders for the browsers you removed inside your .config directory (or snap directory for chromium) that may have some configuration still overriding? If so, you could delete those directories and see if that helps.
take a look at 'Welcome' application's 'Browser Selection' to see if there is anything not set correctly. May be you have to click on 'Make default' for firefox again?