Just asking if someone out there has seen the same quirk:
If I want to drag a file to a dropzone in a website (say gmail's compose interface) Unity brings up the window picker bar (Launcher) and I can't drop the file in the webpage. It's like nothing happens.
I haven't seen if it happens in Firefox too, just tried it with Chrome.
I had the same problem with chromium when i want to upload files with drag and drop.
I suggest you do this trick: start drag your file and select the Chrome window with Windows(Super)+Tab. Finally it will focus you the chrome window and hide the Unity Launcher, so you will be able to drop your file correctly.