Google has announced that it is open-sourcing it's popular Browser Sync Add-on and abandoning further development in favour of popular alternatives like Mozilla weave, Foxmarks, etc.
For those of who don't know, Google Browser Sync let you synchronize your bookmarks, cookies, history and passwords across multiple computers.
The code is available here. Or if you are simply curious just browse through the code online. If you are learning to write your own add-on for Firefox, this is great opportunity to see how coders at Google write their code.