This is chrome's default behaviour, and is used by chrome themes to support patterns.

I believe this contradicts how Lightweight Themes worked previously.

It does, and if we don't take care of that, it'd be very jarring visually. We should tread carefully here!

I don't think this is a problem. AMO enforces a huge minimum size for the headerURL, so the repeating parts would probably never show. If it does turn out to be a problem, then we can check if the prop name specified is theme_frame, and repeat in this case. However this adds significant complexity...

(In reply to Tim Nguyen :ntim from comment #3) > AMO enforces a huge minimum size for the > headerURL, so the repeating parts would probably never show. What's the point of repeating it then? Is AMO going to drop its minimum size requirement?

(In reply to Dão Gottwald [::dao] from comment #4) > (In reply to Tim Nguyen :ntim from comment #3) > > AMO enforces a huge minimum size for the > > headerURL, so the repeating parts would probably never show. > > What's the point of repeating it then? Is AMO going to drop its minimum size > requirement? The minimum size requirement is for lightweight themes, not WebExtension themes. Mike and Jared are concerned about lightweight theme compatibility, but I don't think it'd make a difference for those LWT. However, it will make a difference for WebExtension themes, by allowing more Chrome compatibility.