[gourlaysama]

On Firefox you can go to `about:processes`.

It lists tabs by process, and includes the PID (on Linux; no idea about other platforms). You can also directly kill tabs and processes from there.

[dmos62]

That's super useful on a resource strapped system. Wish I knew this earlier.

[nine_k]

For a resource-constrained machine, uBlock Origin + Auto Tab Discard save a lot of resources and keep a window with 100 tabs quite usable.

[rstuart4133]

You should take a look at Firefox's about:about. There are all sorts of goodies in there.

For example, about:compat lists sites they added hard coded work arounds for.