Fullscreen in Firefox's picture-in-picture mode doesn't work
1. Make sure PIP is enabled in Firefox, then visit a page with a video (e.g. https://www.w3.org/2010/05/video/mediaevents.html)
2. Click the PIP icon, then click the Fullscreen button in the bottom right or press F:
The button works in KDE Plasma and GNOME, but not XFCE. I noticed when you right click the PIP window, Fullscreen is grayed out in the menu, which is probably why it doesn't work:
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