I have just upgraded my Sony Xperia Z Ultra to a Xiaomi Mi Mix. I have off course installed firefox but compared to my old sony it seems to be using the phane ui and not the tablet ui although the display sizes are the same: 6,4 inches. The difference that might trick firefox up is that the resolution on the sony is 1920x1080 whereas the xiaomi is 2040s1080. I really, really prefer the tablet ui on these big phablets so really hope you can help get this sorted