YouTube's "Save to Watch Later" popover menu has been broken in Firefox for years (at least on my Linux installations). The three-dot menu → "Save to Watch Later" doesn't respond to clicks. Other popover menus work fine (account menu, upload menu), but this specific one is broken.

I reported it on Twitter/X (YouTube staff responded asking for feedback), submitted feedback through YouTube's website, but it's still broken as of December 27, 2025.

My workaround: Copy video URL → Open Chrome → Save → Switch back to Firefox. Very inconvenient when Firefox is your main browser.

I finally built a userscript workaround that fixes this for me:

  - Adds a direct "Watch Later" button to the video menu via DOM injection (bypasses broken popover)
  - Saves videos to localStorage and automatically saves them when they appear in recommendation sidebars on other pages
  - Injects pending videos directly into the Watch Later playlist page DOM (shows them at the top with clear "not saved yet" indicators)

Why this approach? YouTube has complex authentication checking, so you can't simply send a POST request to add videos to playlists. Instead, the script waits for videos to naturally appear in recommendation sidebars, then clicks YouTube's own "Watch Later" buttons (which DO work in Firefox when hovered).

Works in Firefox with Tampermonkey or other userscript addons.

Code: https://gist.github.com/beenotung/6cfb46bd5f4f800ac539331753...

Sharing in case other Firefox users are experiencing the same issue. I hope YouTube will eventually fix this and make sure it works not just in Chrome, but until then, this script works for me.