How to Reverse a YouTube Playlist in Firefox
Most playlist-reversing extensions are Chrome-only, which leaves Firefox users hunting for an add-on. The good news: you do not need one. A web-based playlist tool works in Firefox (and every other browser) with nothing to install.
The no-add-on method
Open playlist.tools in Firefox, paste the playlist URL, and sort by date, oldest first. The playlist plays in reverse (chronological) order immediately — same result as a Chrome extension, no installation, and it cannot break when the browser updates.
Everything else works in Firefox too
Because it is a regular web app, all features work the same in Firefox: sorting by title, shuffle, marking videos watched, progress tracking, and cross-device resume with a free account.
You can do all of this free on playlist.tools — paste any playlist URL and start sorting and tracking in seconds.