Edit: sadly, Auto Tab Discard did not fix my issue. Firefox is also set to block audio (including video with audio to my understanding) by default, which I never changed so I don't think that helps with this issue either.
So I installed pop on my laptop a few months ago, and recently got another one where I installed arch. On both laptops I mostly just watched series, and often times I'd just leave the laptop with the media player still open.
Now to the issue: Randomly throughout the day, it would just start playing whatever I left open, usually after a few hours of being left alone. Now that I think about it, I think it was only crunchyroll. Does anyone experience anything similar, or might even have an idea as to how to fix this or what causes this? Is it just crunchyroll being buggy?
If it's just Crunchyroll doing this, you can disable auto-play for it (or just disable it for all sites, IMO automatic playback of media is pretty annoying).
Another alternative is to use Auto Tab Discard, which automatically suspends tabs which are inactive after x seconds. This also helps save memory and CPU usage, and also greatly benefits laptop users. So if you tend to leave your browser open and have dozens of tabs in the background, I'd highly recommend getting this.