Facebook Messenger has just been released for Mozilla's Firefox, offering users a persistent toolbar from which they can chat with friends while browsing the web. The experience largely mimics what you're used to from the social network, with realtime notifications (for comments, photo tags, and other events) also displayed. Messenger is the first product that has stemmed from Firefox's Social API, which Mozilla first began work on in March.

"Social activities go well beyond sharing," the company said at the time. A behind-the-scenes look at the development of Messenger for Firefox shows Facebook was also eager to integrate its product even deeper in the core browser experience. "Facebook was a natural early partner, having a mature chat product as well as lots of dynamic content in the ticker and sidebar," says Pamela Vagata on Facebook's engineering blog. Other companies have been working to tighten the bond between daily web activities and social sites: Bing, for example, has sought to complement search with customized data from Facebook, Twitter, Foursquare, Quora, and other services.