Currently, support.mozilla.org only has a light theme. Since its main content is text (questions and articles), most of the website is white, which makes SuMo usage in the dark really unpleasant. A dark theme would help a lot
Since there is no way to exactly determine whether the image is AI-generated (unless it has been generated by your own service), the only implementation I can imagine is an add-on, but it would still be inaccurate.
Firefox already has a "System theme — auto" theme, which should follow your system theme (light/dark).If that doesn't work for you, please ask a question on SUMO.
And if Firefox is closed and you're starting a web app, the main Firefox process seems to be triggered as well (which may be explained by a chosen implementation, but still feels weird).