This is very much a "1.0" release of the new UI; we definitely have a lot of polish and features to add still. For the first release our focus was on getting the fundamental UI and performance work done. The nightly builds from http://nightly.mozilla.org/ are much more polished already.
The nightly tab interface is a lot better, with the tab close buttons on the right. Previously with the tab expander button in the top right and the close buttons on the left edge, closing tabs meant reaching all the way from one corner to the other side of the screen, which is not always easy or possible with a single finger.
I think you should definitely pursue tweaks that reduce the amount of finger movement required to do common tasks. Just to steal one example from Opera, when you long-press a link, the context menu appears directly under your fingers, so you don't have to go anywhere to get to it (similar to the right-click menu on the desktop). This is incredibly convenient, because navigating the context menu doesn't cause you to lose your place on the page.
I'm hoping for something like the stock browser's quick controls myself. I find them much easier to use quickly, and even a little bit of extra screen space is nice to have on a phone.
This is great. Keep up the fantastic work! The FF mobile team deserves a lot of kudos for the way they've been able to fight their way back onto Android. I remember it was kludgy beyond belief as much as 6 months ago. But since then, it has improved massively with each release.
[I am a mobile Firefox developer.]