[Users] Opening link in Firefox

[Michael]

This setting should be accessible from the firefox preferences window
 Edit -> Preferences -> Tabs -> Open new window in new tab

btw if you need something more complicated: It is always possible to put path to a custom shell script into the 'browser' field, and then have that script decide what to do based on the URL (or whatever.)
A wrapper, that is. For example, i mangle URLs to cut off some tracker data.