You do not have to disable Firefox Screenshot, just keep using the Mac screenshot utilities.

As a footnote to Tyler's post, the Firefox Screenshot feature should not intercept the MacOS keyboard shortcuts for screenshots. If you run into that problem, could you let us know what keyboard shortcuts are being intercepted?

(I used this article for reference on the MacOS keyboard shortcuts when I had a Mac briefly: https://www.itg.ias.edu/content/keyboard-shortcuts-capture-screen-shot-mac-os-x.)

The keyboard shortcuts are Cap Command 4 for selection screenshots and Cap Command 3 for entire pages. Those shortcuts are something else for Firefox, so it is not possible simply to override the FFox system. It is awkward only when I am in fullscreen mode, which I often find convenient. With the image reduced, I can always resort to the FFox system. For the moment, if I expect to want to capture full-screen images, I go to a different browser, where the MAC screenshot system applies. Many thanks for your contribution.

Hmm, Command+3 and Command+4 would activate particular tabs in the current window, according to:

https://support.mozilla.org/kb/keyboard-shortcuts-perform-firefox-tasks-quickly?#firefox:mac:fx61

But when you add the Shift key, that function shouldn't be called. I don't see any built-in function that would be triggered. Could one of your add-ons be creating those additional keyboard shortcuts?

With some embarrassment, I went back to Ffox, where I had had problems trying to screenshot using the MAC system. This time, the Cap Command 4 worked beautifully as did Cap Command 3. There was no interference from using those key commands. Infinite thanks and apologies.

I'm glad to hear it works now!