Here is my situation: I'm creating a custom CSS style sheet for the Duolingo website. I've changed the background colour for most elements, including the body. Now, when I click on a lesson in Duolingo, it brings up a loading screen (which does not have its own URL). That loading screen has a background that was not changed along with the body of the website, and so I need to inspect it in order to find what the class name of its div is. I don't have the time to do this, as it switches too quickly to the lesson screen.
My solution would be to manage to put the website on pause, or somehow instantly take a snapshot of the current HTML, before it switches to the lesson screen. How do I do this in Firefox?
By the way, stopping the page from loading is not an option, because the page is already loaded when the "Loading..." screen appears before the lesson. Anyway, I'm under the impression that this change is automated via JavaScript.
I'm running Firefox Developer Edition 96.0b3 on Debian GNU/Linux 11 (bullseye).