Comment # 5 on bug 1206285 from Stefan Hundhammer

As you correctly observed, another, completely unrelated problem, is that
annoying error pop-up that you get for every single keystroke as you try to
enter a path into that combo box. That makes it almost impossible to enter text
here.

It really shouldn't do that after every character entered; event handling is
much too simplistic in that module. And I wonder why it even posts that pop-up
since the same error message is ALSO displayed in that great big text area that
would normally hold the file content.