Not sure about the container connection, but Firefox also now has 'about:performance' which is pretty much like 'top for browser tabs'. When things start getting bogged down I can now find the culprit and nuke it.
about:memory is also useful, it allows you to force garbage collection on the browser as a whole.
Was not aware of those. My observations were mostly noted while trying to figure out why one specific browser wouldn’t simply not sync any custom containers. And then I noticed my fans spin up on my macmini. I only used system monitors at the time before just disabling the add-on.
I’ll definately look at those in the future. Didn’t even know they existed.
(There's an experimental sidebar extension that works better and gives a graphical history, but I'm pretty sure it's unfinished and unavailable for general use. Hopefully it'll come out sometime.)