I understand that implementing this directly in the browser has dependencies and is quite technically complex, but is creating an official add-on just as complex?
Support casting. The system wouldn't let me upvote the other suggestions on this topic, so I'll create a new one. As it is, when I want to cast, I use Chrome. Let us cast, please.
Proper Chromecast support requires proprietary Google software and should not be added to Firefox, as convenient as it might be. Instead, we all should be petitioning Google to open up and standardize the protocol. AirPlay is also entirely proprietary. Firefox should not encourage the use of either of these terrible protocols, especially when it requires relying on proprietary libraries in order to do so.