tl;dr: Request for an option “Selected context only” similar to Google Chrome Dev Tools: https://superuser.com/a/1346827
Initially I faced the issue described here: CSP errors with moz-extensions (if you can say so, it’s not really a Firefox problem if I understand that correctly, though I was not diving into details)
I do have few extensions installed, which tend to throw quite a lot of errors in non-typical environments, such as localhost websites. For example, Fake Data extension https://addons.mozilla.org/en-US/firefox/addon/fake-data-haterapps/ tends to throw some CSP errors, but that not only limited to CSP errors generally. This makes the console hardly readable, turning relatively fine working website consoles into a red mess of errors, warnings and irrelevant messages.
I think it is quite important feature to be able to filter out context, from which the error was thrown in JS console. Such way it will be easier to debug errors in framed content, extensions and main website without distracting messages from other sources.
Furthermore, I think it should not be very complicated to implement, but the result is quite valuable. I would be happy to have this feature, even without regards to the initial problem I had with CSP errors cluttering.