How To Edit Your Facebook CommentPieter posted in "Hacks & tricks". 6 years ago
After Facebook removed the “Comment” button, there was a clear risk of accidentally publishing unfinished comments as users are used to pressing “Enter” to start a new line, instead of using the key to submit their comment. Facebook took note of the concern, and added the option to edit your comment right after you posted it. They also added the instruction: “Press Shift+Enter to start a new line”.
So if you want to edit your message, click the X in the top right corner right after posting it. But be aware that the editing ability will disappear after half a minute, or as soon as somebody else comments after you. If that happens, pressing X will only allow you to remove your entire message.