Comment # 4 on bug 1160331 from Fabian Vogt

The issue does not seem to be on the helper side:

COMMAND: GETSAVEFILENAME
OUTPUT: 0
OUTPUT: /tmp/openSUSE#search.html
OUTPUT: \1

I think it's this:
https://www.rosenauer.org/hg/mozilla/file/tip/mozilla-kde.patch#l1583

Just prepending "file://" is not enough to make it a proper URL, it needs
something like QUrl::fromLocalFile/g_filename_to_uri or whatever there is
inside FF code.