Until very recently, Firefox on Linux did not have GPU Acceleration or WebRender. With Firefox 80 and 81, they were added but both were not enabled by default.

Until very recently, Firefox on Linux did not have GPU Acceleration or WebRender. With Firefox 80 and 81, they were added but both were not enabled by default. It may very well be the case that Firefox is not using your GPU. Regarding mixed-DPI displays and scaling, I have not had issues with GNOME on Wayland. Bluetooth Audio also works quite well for me, and it shows device names rather than addresses. I will agree that GNOME tends to be slow to start apps after a while, although it is very quick on fresh installs. I am not sure why that is.