Ubiquity is a very popular Firefox extension that adds a flexible natural language command line to Firefox, and is developed by the folks at Mozilla. It's now out in a more useful new version, with a sleeker look, a more stable core, and the ability to create good looking skins, as we covered here. If you're familiar with using the Awesome Bar in Firefox, it's easy to take to Ubiquity quickly, although it pays to spend a little time learning how its commands work. Now, Mozilla is working aggressively to bring some of Ubiquity's power to Firefox, and has come up with a prototype and demo of how "TaskFox" (Ubiquity's features running natively in Firefox) will work.
According to Aza Raskin:
"As a user experience exploration, Ubiquity has been incredibly successful. Over a million downloads have highlighted the need for the web to be connected more tightly with by the power of task-based interfaces...The thousands of commands written for Ubiquity illustrate a latent desire to be able to write tiny amounts of code that enhance the web in fundamental ways."
You can watch a video demo of how Mozilla intends to translate the way Ubiquity works into native Firefox features here. There is also a list of goals found here.
I've used Ubiquity extensively, and I think the TaskFox implementation of it should be a welcome native addition to Firefox. Command-line instructions like the ones Ubiquity responds to may feel like an anachronism, but they can be very powerful as on-the-fly tools when browsing. For example, in the screenshot of Ubiquity at left, I have begun to type in the command "e-mail" and even before I'm done typing, Ubiquity gives me options for e-mailing content, translating it, converting it to PDF format, and more.
Try the TaskFox demo video out for what you may very well soon be doing in Firefox.