Hi Mathias,
In the latest version of mojoPortal we added special handling to detect the 2 fragments for android phones. I'm not convinced that Firefox OS will ever become a major phone platform with significant adoption, but if needed we will add special handling to detect it. The config setting only works for single fragments but at the moment Android phone is the only one where we needed to add special handling to detect it. So you no longer need to add anything to that setting for android phones if you use the latest version of mojoPortal since we have other detection for it already built in. If Firefox OS gets past its struggles and does start to become widely adopted then we will add handling for it but for now it there exist no phones on the market at all that I know of, there are plans for release in 2014 but we will wait and see if anyone buys them.
Best,
Joe