Fix the "Broken Window Borders" issue in Fluxbox after a Firefox update
Quick note to self again here: if you are a fluxbox user, sometimes after a Firefox update it reopens without the Window Decorations and remain unresponsive to your Fluxbox keybindings. This results in a very ugly result and very annoying experience, but do not despair for the solution is quick and (much) easier than it appears.
Simply close Firefox, right-click the desktop and choose
Restart from the context menu.
The WM will restart from zero, but your session will remain running (I'd save my work just in case). After everything has resumed running, open Firefox again - it should come up normally as ever.
It seems Mozilla has changed a little bit the way that Firefox interacts with GTK / X11 bindings and it doesn't play the same way as before, which is why a lesser-maintained WM like Fluxbox occasionally behaves this way. But no need to go nuclear and reboot the machine, a quick fix like this should be more than enough (in both FreeBSD and Linux it was).