What Firefox tabs take more CPU and RAM, and how to stop it?

Question

When I open Firefox with many tabs, my Linux machine becomes slower, and in "top" I see a process named "Web Content" which takes a lot of RAM and CPU. I guess it is related to tabs running process in the background with Javascript, e.g. Gmail or Outlook checking for new mail.

A. Is there a way to see exactly which tab takes uses the most CPU/RAM?

B. Is there a way to tell Firefox to stop running the background processes in a certain tab (while keeping the tab open)?

Answer 1

You can view which tabs are taking up the most CPU and memory by visiting about:performance. That page will list the performance information for every tab you have open, as well as whether or not it might be slowing down your browser overall. An example on my system from this page:

performance - What Firefox tabs take more CPU and RAM, and how to stop it? - Super User may currently be slowing down Tor Browser.
Full name: https://superuser.com/questions/1424066/what-firefox-tabs-take-more-cpu-and-ram-and-how-to-stop-it/1424080#1424080 (as window 10292199260).
Impact on framerate: 4/10
CPU usage: 14%.
System usage: 4%.
Blocking process calls: 0%.
Measure start: 111 seconds ago.
Processes: 5996 (child)

There is also about:memory for much more detailed debugging information specific to memory.