[BitBucket user: Alain Mazy]
[BitBucket date: 2018-12-21.08:38:45]

When you say "seeing this"; do you mean you see the popup or you observed that some files are missing after the upload.
Actually, the popup shows whatever your browser.  

So right now, next step would be to implement a browser detection in the explorer js code to show the popup only to firefox users (That's probably as fast as writing this phrase).
Second step would be to re-write the file upload mechanisms in the explorer js code too.  I think that last time Seb tried that he entered a JS dependency hell and gave up.