oh I see. Currently I don't think you can but you should be able to soon. Basically in firefox you can modify the way it handles mailto: links as explained here
https://developer.mozilla.org/en/Web...tocol_handlers . The only problem is that currently if you set this up for zimbra it passes the whole mailto:address portion into the to: field. Zimbra does not currently parse this correctly to remove the mailto: portion, but apparently it will in 5.0.19
Bug 39239 – Mailto: link arguments not parsed