I have the same issue. I also recommend using mbasic to browse facebook and messages. I believe that they made that move in preparation to Android Instant Apps

I have the same issue. I also recommend using mbasic to browse facebook and messages. I believe that they made that move in preparation to Android Instant Apps. (https://developer.android.com/topic/instant-apps/index.html https://developer.android.com/topic/instant-apps/index.html) In the future this button will most likely open the instant version of the messaging app instead of redirecting you to the store.