I'm not sure, but this could be related to playing media files with DRM.
If I recall correctly, last year, when I visited any news post on https://www3.nhk.or.jp/news/easy/on Debian 9 using Firefox ESR, the browser would ask me to enable DRM. If I answered NO, then I would see the
“Your browser does not support the playback of this video.
Please try using a different browser.”
message (or a similar message) instead of videos, and the audio player would display blank (the player that should show up when clicking the big dark blue button that says ニュースを聞く). If I enabled DRM, the media would play fine.
Visiting the same website now that I use IceCat on the Guix system I get the distorted sound in videos and no audio player.
I wonder if people using IceCat in other distributions have the same problem. I was going to report this issue to Gnuzilla, but it seems their mailing list is not very active.