You can also try these related scripts:

• Disable video autoplay in messenger - To play the video just click the play button in the bottom controls bar :)
• 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
• Side bar facebook tweaker - auto-hide side bar right & left drop-navigation logging out