Volume slider missing inside inmersive videos

[javifernandez]

Is your feature request related to a problem? Please describe.
There is a lack of control when using immersive mode on videos.

Describe the solution you'd like
Firefox Reality had a slider setting to adjust volume, while Wolvic browser just mutes and unmutes

Describe alternatives you've considered

Additional context
This is just when in immersive mode for videos.

[svillar]

The volume slider was removed in favour of that mute/unmute in 3afa755 because apparently the media session lacks the volume control ability. We might recheck it