Facebook has given up on desktop messaging. Yesterday, Facebook Messenger for Windows users received warnings that the program would no longer be supported after March 3rd. Today, users of Facebook Messenger for Firefox began receiving the same message.
Users will have to use Facebook’s website to chat after Facebook Messenger for Firefox add-on gets discontinued Monday. Windows 8.1 users can download the Facebook app from the Windows Store to dock as a makeshift messaging app.
Source: The Next Web