Thanks for submitting an idea to the Mozilla Connect community! Your idea has been shared with the PiP team, and we're happy to report back that the feature is actually 'In development' at the moment. A Product Manager will add more information to this thread shortly.
Please keep the conversation going and stay tuned for updates 😃
-The Community Team
Mute/unmute button is already available in Firefox Nightly, and we're going to make it available in the release in Firefox 101 in early June.
Here's a ticket you can follow in Bugzilla to see when it's going to be released:
Great job all around! This idea has now been delivered—the feature is available in the new Firefox 101 release that went live earlier this week (5/31).