One thing you could try is to disable each extension one at a time to see if one is having more impact than others. Unlike chrome which creates an instance in the task manager for each extension and tab Firefox is written to not be a resource hog which is why you don’t see more than one instance in your task manager.

I'm not seeing 'any instances in Task Manager. I've got 9 tabs open and it doesn't show any information about them anywhere I can find.

And why is it so hard to find it? It's not in any dropdown window, why not?

In recent versions of Firefox, the about:processes page can help you map Firefox tabs to specific Windows processes listed in the Windows Task Manager. I don't think that was very clear in the older versions.

And why is it so hard to find it? It's not in any dropdown window, why not?

The Task Manager is at

menu button > More > Task Manager

I think right now to open about:processes you need to type or paste that into the address bar and press Enter/Return to load it. But I haven't checked every menu...

They have been moving "Task Manager" around a few times with the new Proton design. In 87 "Task Manager" is moved to the Help menu, but this is reverted in 88+ and moved once again to the Tools menu under "Browser Tools". In 88 with Proton disabled it is not present under "Tools -> Browser Tools", but only present under the "3-bar" Firefox menu button drop-down list -> More. In 88 with Proton enabled and in 89+ it will be present once again under the Tool menu (Tools -> Browser Tools) and under the "3-bar" Firefox menu button drop-down list -> More.

In all these version you can find it on the "Help -> (More) Troubleshooting Information" (about:support) page under "Application Basics -> Performance -> about:performance". So only in Firefox 88 with Proton disabled (browser.proton.enabled = false) it is hard to find.

• 1691140 - Move "Task Manager" to Tools/More tools [88]
• 1690359 - Move the Task Manager from the "More Tools" menu to the "Help" menu and put Policy items at the bottom of the "Help" menu [87]

(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)

OK, but what is Proton, and why would it be disabled, as it must be, since Task Manager is not under the Tools menu.

And why do the memory usage figures in TM, be 20 or more times less than what I see in my iMac's Activity Monitor? If all the pages were using as tiny amount of RAM as the TM shows, I'd be whizzing all over the place! Not sure how these figures are of any use whatsoever..

Proton is the code name for the new user interface redesign that will be enabled in the next Firefox version. This means that a lot of changes to menus and context menus can be expected and some of these changes are already visible in Firefox 87 and 88.

• https://www.ghacks.net/2021/02/16/firefox-89s-user-interface-will-be-leaner-and-less-convoluted/
• https://www.ghacks.net/2021/04/03/firefox-proton-design-refresh-is-almost-ready-here-is-what-is-new/