YouTube Section Looper (opensource) by Sudhir Babu Nakka

YouTube Section Looper is an opensource project that adds a small control panel directly on YouTube watch pages. Set the start and end timestamps (by button or manual entry), choose how many times to repeat, and play the loop automatically. Settings are saved per video so you can return later and continue looping.

Update (25 Mar, 2026):
Added a 'Adv' button which expands UI to show options to control speed and pitch (simple pitch shift linked to speed control, not studio quality)

Update(29 mar, 2026):
Ability to bookmark yt url's along with looper configuration. eg: Set the looper section times, number of loops etc.. and bookmark the url (using the looper star icon or usual firefox bookmark action). The url now contains information which looper will use to preload the loop section details.

https://github.com/sudhir-asuracore/firefox-youtube-looper

(content looper, video looper)