With the last release of Firefox, Mozilla introduces Firefox’s new Social API with a preview of the first social integration with Facebook Messenger for Firefox.
This was previously only available in the Firefox beta channel. The Social API allows social services like Facebook, Twitter, blog networks or even news sites to easily add persistent social sidebars, toolbar notifications and chats to the browser, no matter which site a user is currently looking at.
How to install your Own Facebook Notification and Messenger on Firefox:
1: First, install or Update your browser to the Latest Mozilla Firefox version
2: Go to this Link Facebook Messenger for Firefox and click on the “Turn On” button.
3: You have the possibility to disable the chat sidebar and desktop notification by clicking on the Facebook icon.
One thing noting about this latest version of Firefox support for Mac OS 10.5 Leopard has now ended.
If you are still using Leopard, You will have to stick to the older version or switch to another browser.