I have strange behavior in Firefox.
When I try to drag file (e.g. pdf, mp4 html) into Firefox, it say in the main window ‘Server not found’ and some crazy Japanese characters. In the address bar I have http:// and afterwards the same Japanese characters.
When I was using OpenSuse 13.2 it work normally - I could drag and paste any file Firefox recognized.
Interestingly, I can confirm your finding logging in with IceWM on the VM “KDE” install: same error and “Japanese” characters.
BUT logging in IceWM in my main “Gnome” install, everything works as expected.
So it seems that the culprit is hidden in some difference between the “KDE” and “Gnome” standard install, not in the WM proper.:\
Tried to update Firefox to 44.0.2 to no effect.
Tried to remove mozilla-kde4-integration (this is NOT installed in Gnome, of course) to no effect.
Looks like some quirks happening when interpreting pairs of UTF-8 characters as single UTF-16 characters, but I could not find a pattern so far.
Opening the test files in Firefox by its** “Open File” command works as expected**, so it seems just a “Drag’n’Drop” problem.
BTW LibreOffice tells me that the strange characters are “Chinese-simplified”, not really Japanese (don’t call on me to assess this lol! )