(In reply to Brendan Dahl [:bdahl] from comment #1)
I looked in to this a bit and it's really up to us on how we want handle negative coordinates in headless mode. Since headless doesn't have any OS menu bars the available rect is the same as the screen size.
Couple of options to make the test pass:
- Allow going negative by adding a fake menu bar space
- Only allow the window to be moved within the screen bounds
- Mix of the above to mimic each platforms behavior
I'm currently checking which web-platform-tests can be re-enabled and stumbled about this remaining problem again. IMHO we might want to respect the platform behavior to give Firefox the same behavior in headless and non-headless mode?
How complicated would it be to get it implemented?