Luca said "for now to only a few **Windows 10** PCs". Moreover, the PDF association is reset. I guess the operating system detected that we try to take over the association and reset the association. We should not try to take over associations on Windows 10.
Bug 1652412 Comment 19 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
Luca said "for now to only a few **Windows 10** PCs". Moreover, the PDF association is reset. I guess the operating system detected that we tried to take over the association and reset the association. We should not try to take over associations on Windows 10.