VideoDetector от einKnie

The addon currently supports youtube.com, vimeo.com, orf.at, vivo.sx, twitch.tv, and netflix.com.

While the addon is active, it will monitor any Firefox tabs on a supported site to detect if a video is playing.
Whenever a video starts playing, the title of the repective tab is changed to contain a custom string. The addon also comes with a toolbar button to quickly suspend and resume the operation, or access the settings page.
On the settings page, you can change the custom string as well as disable operation on specific domains.

Example

By setting the custom string to "Playing ~ "

JavaScript Crash Course For Beginners - YouTube

becomes

Playing ~ JavaScript Crash Course For Beginners - YouTube

The custom string may contain any symbols that the Firefox titlebar can render.
That means, standard emojis like ☺️ or 🖤 are possible. Additionally, you can specify the positioning of the original video title with (%title%). If no (%title%) attribute is set, the string is added before the original title per default.

Example

By setting the custom string to "(%title%) 🖤"

JavaScript Crash Course For Beginners - YouTube

becomes

JavaScript Crash Course For Beginners - YouTube 🖤