Hi Bernard,
Thanks for the finding this. It helped me out too.Found a similar problem in that Firefox-Esr wouldn't open appstream urls in KDE/Discover. Tried the same thing with Chromium and it opened as expected.
After finding this bug report, I installed desktop-file-utils and Firefox-Esr opened the appstream url as expected in KDE/Discover.
Tested using appstream://org.kde.dolphin.desktop Thanks Sheik
