On Arch Linux, Gnome 3.36.2, mesa 2.20.1, 200% HiDPI laptop screen, using webrender.

Going in Gnome "activities" view / Expose, with just the main (laptop's) HiDPI screen results in a flicker of the Firefox window, same happens on leaving Expose.

When plugging in an external monitor, non HiDPI, and dragging Firefox from Expose from the HIDPI screen to the non HiDPI screen, Firefox reacts correctly to the new scale but the window size is reduced to a quarter of the screen despite still being in a maximised state (the window needs to be un-maximised and maximised again).

On youtube, when going full screen on the HiDPI screen, the video and its UI briefly over-scale to 400% before settling to the correct 200% scale. If I set my UI scaling to 300%, the "over-scaling" seems to go to 900%, etc.

I don't know if these issues are the same or if they deserve their own separate bugs.

Also, when plugging in the external screen, the FF window remaining on the HiDPI screen sees its size doubled in height and width despite still being in a maximised state (the window needs to be un-maximised and maximised again).

Do you still see it?
Thanks.

No, this can be closed.