No longer supports upgrade . Please see https://addons.mozilla.org/ru/firefox/addon/boost-youtube/.
I make addons for self. I try make it max small and simple. No spy ware.
Sometimes, youtube API response that maxresdefault.jpg thumbnail is not, but it is.
The addon on any Youtube video player page, in address bar, add button with link to maxresdefault.jpg.

Install

• License: Mozilla Public License 2.0
• Weekly downloads: 0
• Average daily users: 40
• Rating: 5/5 of 4 ratings
• Created: 2017-10-20 22:12:10
• Last updated: 2017-11-12 10:00:10
• Homepage: https://github.com/rty65tt/yt-open-thumb
• Support site and email
• Orig: https://addons.mozilla.org/en-US/firefox/addon/openyoutubemaxresdefaul/
• API: {80ef51c8-994a-4f9b-b840-bcd8c52d8198}