[dahart]

Firefox knows where all its windows are, of course, but that’s not the potential issue being raised. The problem is allowing untrusted javascript access to that info. Luckily, Firefox doesn’t do that, it only allows you (JavaScript author) window information for the windows you’ve directly opened in code.

[boudin]

Actually I don't think Firefox knows the position of the window in Wayland. I thought that coordinates of windows were considered as a compositor concern and not shared with the client.

[bandrami]

Not on Wayland it doesn't. Nor does it know if either window is visible, nor if it has been damaged since the last render.