Right now it appears that the 856 links open in a new tab/window from the OPAC Normal view but not from other pages. It needs to work the same way from the Staff Client as well as the OPAC marc view.
The links open in the same tab for the OPAC Normal View and the Staff Client, so this has already been fixed.
Reopening this because, as the title suggests, it would be great for 856 links to open in a new tab for both the OPAC and the staff interface. At the moment if you open an 856 link your Koha page gets replaced with the 856 link. We already do this when viewing linked authority records.
We have OPACURLOpenInNewWindow. We could add the same for the staff interface or we could make a coding guideline that all links to external sources (not Koha) should open in a new tab. For this to move, it would to know it would be good to know where we have links not following the pref.
Perhaps a StaffInterfaceURLOpenInNewWindow option is the way to go. We'd have to do frequent regex to confirm the link is actually external (not Koha) which may have unintended consequences, and caused unexpected behaviour. At least with a preference people can see a clear on/off for this.