Interconnected devices are becoming more and more ubiquitous, with TV-connected devices such as Chromecast being easily controlled from any phone, tablet or computer with a Chrome browser installed. This remote play feature is now being made available for Firefox on Android, similar to YouTube remote play.
A new icon will pop up on Firefox for Android that will allow you to share any currently playing video to connected Roku and Chromecasts on the same network. You can then control playback of the media from inside Firefox for Android.

This function is available right now. If you don’t already have Firefox for Android, you can grab it from the Play Store.