In my opinion, people could forget which tab plays PiP video. Is not this
video playing mode designed to cases, when user read other pages, for example?
Person could click backward button, refresh button, enter address to urlbar or
close tab, which play video. In fact, video is played in separate window.
Solution:
Warn, when page playing PiP video will be closed.
I mostly use PiP mode with YouTube so I don’t face this problem but I can definitely see this as a problem for sites where you use PiP for a video on the page and then on that same page, you are reading something, get distracted, and then navigate from the page that is actively in PiP mode. I agree that either some warning or visual cue on the tab itself can probably help with this scenario. I think Mozilla needs to buckle down on the the PiP mode sticking around for future releases as a usability feature and as such needs to consider how this can be added to it.