Ultrawidey provides an 21:9 aspect ratio to a lot of video streaming services, like Youtube and Netflix, it requires no button presses it fits your screen automatically.
Please note that videos with a black border can be removed by pressing ‘Z’.
Press 'X' for forcing the 21:9, this might be useful on some sites.

Install

• License: Mozilla Public License 2.0
• Weekly downloads: 14
• Average daily users: 193
• Rating: 3.8148/5 of 27 ratings
• Created: 2017-11-26 21:47:42
• Last updated: 2019-01-07 21:30:10
• Homepage:
• Support site and email
• Orig: https://addons.mozilla.org/en-US/firefox/addon/ultrawidey/
• API: {f400f50e-a470-49be-94cc-e0141471478a}