Comment # 17 on bug 1103835 from Sebastian Kuhne

Today, with TW 20180920, the issue appeared again.

Firstly, echo $XDG_DATA_DIRS resultet in 
/home/sebastian/.local/share/flatpak/exports/share:/var/lib/flatpak/exports/share:/usr/local/share:/usr/share
that is exactly the same as reported already above.

Then, I have updated all gtk2-/gtk3-packages.
Results:
- same behaviour (Firefox did not start, LibreOffice did not start)
- same echo output

After that, I have forced sudo zypper in -f gsettings-desktop-schemas.
Results:
- Applications do start now
- same echo output

In summary, $XDG_DATA_DIRS shows always the same results independent on any
forced installation. ONLY the forced installation of gsettings-desktop-schemas
solves the issue.