xdg-desktop-portal-lxqt (xdg-desktop-portal backend for LXQt)

A backend implementation for xdg-desktop-portal that is using
Qt/KF5/libfm-qt.

Use LXQt filedialog in applications:

 - Firefox version 98 and higher: Open in the address bar about:config,
search for "portal" and set both widget.use-xdg-desktop-portal.file-
picker and widget.use-xdg-desktop-portal.mime-handler from 2 to 1.

 - Thunderbird: Preferences > Configuration Editor
 widget.use-xdg-desktop-portal has to be set to 1.

Some other GTK applications can be started with GTK_USE_PORTAL=1
application

A general use of GTK_USE_PORTAL=1 in ~/.profile or /etc/profile can
lead to issues and is not recommended.