I'm quite sure most of us use facebook or at least have an account. At this moment facebook really likes everyone to install the facebook messenger app. You cannot send messages from the normal android app and even in the mobile website it will redirect you to the play store to install the app.
If you would first request the desktop version (see picture below) and then click on the messages part in the mobile facebook website, then you can send messages to your friends without installing facebook messenger!
If you also would like to uninstall the facebook app, you can click add to homescreen (also see screenshot below) then the facebook website will show up as an icon on your home screen and after you click it not the app will open but the mobile website it is even possible to enable web notifications to get notified when you received a message or a post on your wall.
click on the three dots in the top right corner to open this menu in google chrome on your android device