Firefox is once again the leading web browser, now that they’ve caught up with Chrome’s multi-threaded approach for tab management. Where Chrome still has an edge though is its built in Task Manager window, showing you the resource usage of each individual tab. Yes, Firefox has the about:performance page, but in my experience it isn’t good at showing me which tab is causing my laptop fan to do a jet engine impersonation, so how to proceed when I want to cool things down?

Fortunately, Firefox’s threads are separated out in the macOS Activity Monitor. Note that I have ordered the view in %CPU descending:

macOS Activity Monitor

Whilst there’s no way to match a particular ‘FirefoxCP Web Content’ process to a particular tab, if you highlight the one that’s using the most CPU time, click the ‘Quit’ button at top-left (the one with a white X on a black circle) and select Quit on the dialog, you will kill that one process without bringing down Firefox itself.

How to know which tab you killed? Well, switch back to Firefox and cursor through your open tabs. When you reach the one you’ve killed, you’ll see a “Gah. Your tab just crashed.” message, with a handy ‘Reload’ button, so if it was one you absolutely didn’t want to lose all is not lost.

That’s it! Obviously the approach I’ve described here uses a Mac’s Activity Monitor, but I expect there are equivalent ways to achieve the same on Linux. I don’t think Windows offers adequately fine-grained process control, but I’ll be more than happy to be contradicted in the comments!

N.B. The astute will notice that there are far fewer FirefoxCP Web Content process than you have open tabs. I don’t know how Firefox metes out threads to tabs, but in my experience with this approach CPU-hungry tabs always seem to have a process all their own; I’ve not yet had one process kill take down multiple tabs.