Firefox no sound?

I noticed yesterday that the Firefox sound doesn't work, I can't hear anything with other apps, that's not the case, e.g. Netflix or others, how can I change that (?

(I had already tried restarting)

Open Firefox and then right click on the loudspeaker in the lower right corner, where you control the volume. Then go to the volume mixer and see if Firefox is muted.

Many Thanks! Worked!