It's entirely possible that Ubuntu is not compiling in stylo at all. In fact it's likely: Firefox nightlies on Linux have been shipping stylo (preffed off) for

It's entirely possible that Ubuntu is not compiling in stylo at all. In fact it's likely: Firefox nightlies on Linux have been shipping stylo (preffed off) for close to three weeks, so if a two-day-old Ubuntu build doesn't have it, chances are neither will a newer one until they change their build configuration to use --enable-stylo.