Mozilla 1.2a is available now. It includes an improvement on keyboard navigation:
Type Ahead Find is a new feature that allows quick navigation when you type a succession of characters in the browser, matching the text in one or more links on the page. To give it a spin just go to a web page, start typing and hit enter to load the selected link. You can also use it to search for any text on the page by typing / before your search text.
Also, while upgrading to it I noticed that the preferences toolbar has been updated; now it allows setting the user agent.
I downloaded rv:1.2a and I can not find where to change the ua anywhere in the browser itself. I have done it the old way with user.js but what your describing sounds easier. Where is this option hiding?