Thank you so much M4D_MAXX_, glad it's working for you! And great tip on the about:config fix for background audio!

To answer your question about the volume control position: it actually depends on where you're watching the video. On the homepage feed, the volume control appears in the lower right. On Reels (fullscreen), it sits in the upper right alongside the playback bar. On Stories, the controls are at the top. So the position isn't something you change manually, it just adapts to the current view automatically.

Fullscreen support is noted and on the radar for a future update!