Like I said, I narrowed it to be a win10 "feature improvement" and not a FF problem. But I need to know what exactly FF is expecting from the OS when the "Open Containing Folder" button is pushed in the downloads window. BTW the Open Containing Folder does not exist any more in win10, at least to my knowledge. I had to create new right click menu entries to recreate "open file location" functionality like in the previous MS OS. My OS is win10 Home vs 1703, build 15063.332 deCrapified. And NO I am not interested in any other updates from MSh#t, I jut want to make it work with FF downloads somehow.