Hello
I have another problem with drag and drop, it may be a bug but... I
don't know how to trace it precisely. 
Generally in Firefox until version 48, dragging an URL icon (favicon in
address bar) to desktop caused opening a menu which allowed to save or
link (create .desktop launcher) to a site. This still works in later
versions of Firefox in XFCE and MATE, but in TDE since version 48 it
started to behave differently: Now Konqueror asks for filename, and
then saves just a text file with url as text, and these files are
unusable as launchers. 
This is probably not a Firefox problem, as this dragging still works
well in MATE and XFCE without problems. The problem is present only in
TDE. Is it possible to give a template to... I don't know, Konqueror?,
how to create .desktop file for a specific application or content type?
Or is it a problem with not full drag and drop implementation?
MCbx