User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:80.0) Gecko/20100101 Firefox/80.0

Steps to reproduce:

1. Go to site https://9anime.to/watch/one-piece.ov8?ep=1
2. Play the video
3. Click on Picture in Picture toggle

Actual results:

Picture in picture not started. Nothing happens

Expected results:

Picture in picture should start

Also I have modified couple of settings:
fission is enabled
webrender is enabled
image.avif.enabled true
layers.advanced.basic-layer.enabled true
layers.advanced.fission.enabled true
media.eme.enabled true
media.ffmpeg.dmabuf-textures.enabled true
media.ffmpeg.vaapi-drm-display.enabled true
media.ffmpeg.vaapi.enabled true
media.ffvpx.enabled false

Should I start changing some settings?

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

Picture-in-Picture works inconsistently when Fission is enabled - mainly because on some sites (like the one you linked to), the video is hosted in a third-party, out of process iframe, and Picture-in-Picture support with out of process iframes isn't complete yet.