Firefox has integrated Facebook into their browser. The feature was built on a new Social API for the web. You can set up Facebook Messenger for Firefox at this link. You will also need to update to the latest Firefox browser and then visit the Facebook Messenger for Firefox page and click “Turn On.”
After you enable the feature, you will get a social sidebar with your Facebook chat, updates, new comments, and photo tags. You will also see new notifications for messages, friend requests, and etc. that you can respond to right from your Firefox toolbar.
Below is a video of how it works: