Facebook Messenger for Android has chat heads enabled by default.
You can disable this feature if you don’t like it. Here’s how you do it:
Open Facebook Messenger.
Hit your profile picture in the top left.
Disable “Chat Heads.”
Follow the steps above to enable chat heads. However, you need to enable, not disable, Chat Heads.
Follow these steps to open the chat head for a conversation:
Open the Facebook Messenger app.
Long press a conversation you want.
Select Open chat head.
That’s all there is to it.
You can close the chat head by dragging it and dropping it on the X at the bottom.