When I am replying to a message in Facebook and I press the Enter key it sends the message instead of moving to the next line.
How do I add extra lines in my comments before I actually post the message?
If you have the enter arrow box unchecked as shown in the figure below you will be able to go to next line by pressing Enter. Otherwise it will send your message!
I don't know why Facebook is behaving this way, but you could try pressing Shift+Enter. This should also enter a new line without shifting focus.