Open videos in PiP mode

[AXeL-dev]

The Picture-in-Picture mode API is available on chrome but not yet on Firefox, so the only thing to do is to wait for now.

Or maybe implement a custom PiP mode, using custom windows? like in the Enhancer for YouTube extension. But this may require extra-work and it might be dropped out later when the API will be available, so it looks like a waste of time, don't you think so? 🤔