Make Zoho my default Webmail Link in Firefox

Make Zoho my default Webmail Link in Firefox

I would like to make Zoho my default Webmail in Firefox.  The only two choices I see  is Gmail and Yahoo.  I looked at Firefox config “gecko.handlerService.schemes.mailto.” and it seems I could possibly add one here or edit the Yahoo or Gmail one to point to Zoho.  Before I start messing with the Firefox configuration, just curious if anyone else has an easier solution.  Also, what would be the proper URL to add.  Gmail and Yahoo have the following:

Gmail:  https://mail.google.com/mail/?extsrc=mailto&url=%s
Yahoo:  https://compose.mail.yahoo.com/?To=%s

So I assume Zoho has something ending in a %s