Well, I've been dragging my feet on upgrading my 20.04 LTS system, but it's a slow, laid-back day today, so I decided to move ahead. The entire process took something like four hours to complete. I'm now logged in on my upgraded server, and everything seems to be working nominally.
Except. I saw in the installation notes that Firefox now had to be installed as a snap. I've not been a fan of snaps, but I figured why not? In fact, my favorite browser, Brave is now running much smoother on my system, even receiving updates as it's supposed to.
Now Firefox won't launch. 
The Firefox icon shows in both the panel and in the Internet menu, but selecting either result in the spinning "wait" cursor, the icon appears in the plank, but then just goes away. No launch, no nothing.
I checked the software boutique and ran the snap command and both verify that Firefox is installed and configured.
Not a show-stopper, but just another fail on the part of snap. I may just remove Firefox altogether.