The demo is hard to see because of screen glare, but our UX designer Madhava goes into some detail about the design decisions that went into making Firefox for a mobile phone. One of our big challenges is how to optimize the use of screen space:
For the small screen problem, one of the things we do is when you start to use a page, the controls you don’t need anymore pan off the top of the screen…just by using the page, UI you don’t need goes away.
Uniquely, mobile Firefox takes this one further step by spatially relating browser controls with the page, similar to the URL bar at the top of the page. Controls can be found off the left or right of web content with a quick flick.