In the browser, you can easily close tabs by clicking on them with the middle mouse button, so you don’t have to aim for the small X button.
Maybe this might be sensible in Zammad’s tab bar on the left too? Currently, clicking a ticket tab on the left with the middle mouse button will open a new browser tab with another instance of Zammad, which inevitably breaks the first Zammad instance tab. Closing the ticket tab might be more useful 
Though, when the “you cannot open Zammad in more than one browser tab” issue is resolved at some point, closing the tab instead of opening a new browser tab might not be what the user wants. Thoughts?