The tests were updated on bug 1963047. We should fix this bug.

My patch only updated the manifest file for the correct bug id. I'm not working on a fix right now.

For a fix it would be good to know if there is any property on the prompt which would allow us to retrieve the origin window which opened it.

https://hg.mozilla.org/mozilla-central/rev/bf71f38a0f8a

We need to check if the reference to the frame's window is already accessible or not. Let me check that next week.

I did some investigation here, and I don't think we have at the moment any information about the window/browsing context which opened this prompt in the notification we listened to or prompt object which we receive or can find in the target browser. But I think we can add this information in https://searchfox.org/firefox-main/source/toolkit/components/prompts/src/CommonDialog.sys.mjs#228 for desktop, because this.args contains owningBrowsingContext property which is the browsing context which opened the prompt. For GeckoView there seems to be info about browsing context here: https://searchfox.org/firefox-main/source/mobile/shared/components/geckoview/GeckoViewPrompter.sys.mjs#29, but it also has to be passed down to the right place. Additionally, we will have to refactor https://searchfox.org/firefox-main/source/remote/shared/listeners/PromptListener.sys.mjs#139-214 to work with it, but it can probably be simplified in the end.
So overall I think it should be possible to implement, but we should probably bump it to 5 points.