You can also try these related scripts:

• LennyFace w wiadomosciach na facebooku - dodaje lennyface'y na facebooku
• Messenger+ - Improves the facebook messenger desktop experience
• Toggle Messenger Sidebar - Button to hide messengers list of conversations
• Messenger.com notification - show notifications for every message on messenger.com (still very experimental)
• Side bar facebook tweaker - auto-hide side bar right & left drop-navigation logging out