Since we have a test that checks the `isMMI` path, we need to make the `navigator.mozMobileConnections` object has a 'valid value' at least for one sim, I suggest to add the following line :+1: 
`navigator.mozMobileConnections = [true];`

That's basically to allow to go through the following code path:
https://github.com/mozilla-b2g/gaia/blob/master/apps/communications/contacts/js/views/details.js#L491