Setting the user dirs manually can cause gtk file explorer
dialogs to not open correctly freezing applications that
try to use it.
Firefox had this behaviour after having installed and removed
flatpak adn dependencies which included xdg-user-dirs, strange
because it worked before without it.
It is worth noting that this error does not give any hints or
error message, moreover the gui remains active but unresponding
I found out what caused the error essentially by chance.
Alessandro Mauri