After upgrading to neon 5.15, Firefox now uses the KDE file open/save window instead of the GTK one. However, the KDE file chooser window doesn't remember the name of the file I'm trying to download (the filename is just blank). Does anybody know how I can make Firefox use its original GTK file picker until this bug is resolved? I have been tearing my hair out trying to find a solution, and running "GTK_USE_PORTAL=0 firefox" has no effect.

Okay, so I solved this by editing /usr/bin/firefox (which I didn't realize was just a script). I commented out the line "export GTK_USE_PORTAL=1", and now I have the GTK file picker back. The missing file name bug has supposedly been fixed upstream, so eventually I'll switch back to enjoy the KDE file picker.

The update to "xdg-desktop-portal-kde" that came in today resolves the missing filename issue, so no need to use the GTK file picker anymore. Yay!