Ubuntu users should be getting their Firefox 14 updates today. Firefox 14.0.1 to be exact.
The most prominent change would be secure search which uses SSL for Google searches automatically. Efforts are underway to add support for more search engines but for now this feature is limited to Google.
The day the browser becomes a full gaming platform edges closer, too. The experimental Pointer Lock API is available, making raw mouse events available to the browser. The most obvious application would, of course, be in games. The standard isn't finalised yet so expect things to change moving forward.
The release notes has all the details.