The latest update for Facebook Messenger on the desktop brings a couple of features that are being tested in the beta version of the mobile app. Version 350.5.122.0 will now let you ignore a conversation if it comes from a Facebook friend you choose to ignore messages from. That means you won't get notifications when said friend messages you. Instead, their messages will be moved to the message requests section. The second feature is you can now send voice clips from the desktop app. So, if either feature seems useful to you, now might be the best time to download the app.
Source: MSPowerUser