The main bug fixed here is that in half of our interfaces, we use "is browser frame/element" to mean "browser or app", and in the other half, we use it to mean "is browser not app".
There's a related, functional bug also fixed here, which is that a browser process doesn't inherit its parent's app-id. This causes problems e.g. for IndexedDB: If a browser inside an app uses IndexedDB, the DB should have the app's app-id.
I also modified Tab{Parent,Child} and nsFrameLoader to call "app" "ownOrContainingApp", to emphasize that we might have inherited the app from a parent process. I left nsIDocShell::appId alone, because changing that would have necessitated changing nsILoadGroup and therefore a /lot/ of users in Necko; it's also not clear it would have clarified anything in those cases.
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