Investigate YouTube Music issue with the extension

[aaga]

User reported that Rally extension breaks YouTube Music on Windows 10 (could be an issue on other platforms too). Investigation needed first to determine source and scope of the bug. Fast-follow with bug fix since this is a paid feature.

https://mozilla.slack.com/files/U03TK43VD62/F04G3E0FJCS/img_2355.png

[digitalcircuit]

I consistently encounter this issue with YouTube Music and the modern Rally addon (attention-stream@rally.mozilla.org).

If Rally is enabled, playback fails. The Developer Console mentions mozilla-rally-yt-scanner sending data from YouTube page to content script, so I suspect something about the scanner breaks on YouTube Music.

Once I disable the modern Rally addon (disabling injector.content.ts), playback works for the next YouTube Music page load, and as long as I don't fully refresh the page, I can navigate and play other songs with the addon re-enabled.

Let me know if there's any other information that would help!

System

• Kubuntu Linux 22.04 LTS
• Firefox 111.0.1-2 via Snap
• Various other addons installed (NoScript, uBlock₀, legacy Rally Core, etc) though playback works fine with those.