I really like the built-in Task Manager in Chromium based browsers (Chrome/Edge/Vivaldi):
In Firefox, we have about:performance but it has some shortcomings:
Would love to see this kind of functionality in Firefox!
BTW, you can use about:processes which provides more info. It doesn't have a network column sadly.
Coming back to this - another advantage of the Chrome task manager is that it opens in a floating mini window so you can keep it open while browsing/poking around.
In Firefox about:performance/about:processes are tabs so you can't easily browse at the same time (guess you could open it in an entire new FF window though).
Moreover while monitoring tabs and extensions with Task Manager some entries keep disappearing and reappearing for the whole session giving the impression that this tab is unstable.