That blocks the system entirely. You can't alt-tab quickly and won't see anything that wants to come to forefront. So on top should switch off, when going full screen.
It's very intrusive and very annoying tabs get grouped, when you just try to rearrange them. It should not be happening. Grouping is a very niche feature, so should off by default. It should be just option.
Message Pane visibility should be remembered per folder, as in Outlook. And should not be even visible for Spam, Junk, Virus and similar folders by default.
Instead they removed widget.gtk.non-native-titlebar-buttons.enabled from Firefox 140 at all.....Is there any Firefox fork that didn't or is it time to depart?
