I am no means an expert on this subject, I just did a little research that I think might be relevant for your expert eyes to check out: *https://www.reddit.com/r/kde/comments/1jt0u8/kde_file_picker_in_firefox/ *Previously it was said it was not going to be fixed a few years ago in the official Firefox Linux build here: https://bugzilla.mozilla.org/show_bug.cgi?id=298848 It looks like there are currently only work arounds. Try the KDE forums to see if you can get a recent answer ;)