If they don’t affect you, you can safely ignore them. You will see much more errors in the devtools than are caused by your own code. And finally the documentation only mentions errors that are specific to extension APIs, since this is after all the normal web stack. But I’m sure you’re aware of that.
I have seen your thread on it. Which turned out to be an (unnecessary) event listener that was never removed and leaked when you reloaded a temporary install (or if you were to upgrade your extension). At least that’s what I grasped from your description of the issue afterward.
Error reports and problems can stall for various reasons. I don’t think you should be discouraged by that but instead try to figure out why it stalled (was there some information missing, was it a generic communication issue etc.)
Console.log should work everywhere in your extension code. Please consider https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Debugging on where you’d find the output for a console.log statement. As an example, for your content scripts/execScript
s you’d want to check the page dev tools.
Lastly, MDN is an open wiki. Of course content should be structured, but if you think there’s some information that is glaringly missing, please contribute it to MDN. Note that documentation is a very exact science and you will often find information in one specific place and not repeated any further.