My problem is when I use linux - firefox, the shortcut for closing a tab in zammad, is the same as closing the firefox window.
As it is not easy to change shortcuts in zammad nor in ff, I found another way.
THe zammad bug is already documented here.
I change my user agent OS to MacOS and 
!
I’d like to update the github ticket for others, but I can’t so I post here.
Cheers!