Thanks to Mozilla for breaking things during an automatic update I had no choice to install simply because I tried to use my browser!
Well, I'd downloaded, but I hadn't installed. I think I'll wait on that until the all-clear at this point...
To be fair, the thing that broke was due to an incompatible add-on. I'm just frustrated that the update happened automatically and didn't give me a warning or even a chance to cancel the installation before upgrading to something that was incompatible with what I was using.
Other than my frustration with losing all of my tabs in the various tab groups, the updated browser does seem to run well.
And in the process of trying to find another tab grouping add-on I found one called Multi-Account Containers
which is a little clunky but basically allows you to set up different sessions (containers), so you can be logged into multiple accounts on the same site at the same time. And it even allows you to configure certain websites to open in certain containers by default.
So for instance, if I visit a bunch of gaming websites, such as Wikia and GameFAQs, I can configure those sites to always open in my "Games" container so they don't get in the way of my "Work" container, or whatever.
It's not quite the same as the Tab Groups were, since using the groups would de-clutter my screen and only show the tabs for the active group. But I do like how I can have separate logins/IDs for each container. I don't know about anyone else, but I like to keep identities separate, so I have a couple of different Gmail accounts, etc. Having a "Personal" container and a "Business" container which can both be logged into their own Gmail accounts at the same time, for example, is pretty nice.
Even so, I think Vivaldi is going to remain my primary browser for the time being.