Firefox has been experimenting with autocompletion, it might make it into a future version.
https://mozillalabs.com/prospector/2010/10/27/navigate-the-w... You can install the first-party addon without even restarting your browser. There are other experiments in the "Lab Kit"
https://mozillalabs.com/blog/2010/11/its-time-to-get-your-la...