Update: Firefox Beta now includes this new functionality by default.
I love using Firefox as my desktop browser mostly because Ubuntu's web apps feature is much more stable in Firefox than in Chromium. That said, I always find myself switching back to Chromium for one reason: Chrome on Android is simply a better experience than is Firefox for Android.
I could use different browsers for different platforms, of course, but then I'd be missing out on sync features, which are incredibly handy when using multiple devices.
So, having recently switched back, yet again, to Firefox, I set out to make Firefox on Android a better experience. I found a few wonderful extensions (one of the reasons I love Firefox in the first place- Chrome for Android doesn't allow any customization, let alone addons), and that helped. One major annoyance I ran into was the bounce-back effect Firefox employs when scrolling to the very top or bottom of a web page. It is, to my mind, a highly unnecessary and purely aesthetic feature. It also makes Firefox themes for mobile look very out of place, since the themes don't skin the canvas "underneath" the page that's revealed during the bounce-back; you'll still see the default Firefox blue butted up against the colors of your theme.
So I set out to find a way to eliminate the feature, perhaps through an about:config tweak or an extension. In my search, I stumbled on this thread, in which Firefox developers discuss the bounce-back feature. In the thread, one of the developers has uploaded a patched version of the Fennec browser which eliminates the bounce-back feature.
I downloaded and installed the patched Fennec, and was pleasantly surprised by what I saw. Not only was the bounce-back feature gone, but the entire interface, save the navigation bar, had been upgraded, and the performance was significantly smoother.
If you're not familiar with Fennec, it's essentially a test version of Firefox mobile, like Mozilla's Aurora channel. Most consumers will download the stable version of Firefox, but two other channels are available: Beta and Aurora. Beta is slightly less stable than the stable version, and Aurora is considered unstable, and is the testing grounds for new features.
Those new features appear to offer a much better Firefox experience. Scrolling and animations are smoother, the lines are subtler, and the swipe gestures are a far superior way to access your history, bookmarks, and reading list. Here's a quick video of Fennec in action (cick the image to play):
The current stable release of Firefox is version 25, while the Aurora channel, as of this writing, is at 26.0a2, and the file I installed is version 26.0a1. That means that, if you like what you see, you can use version 26 of Firefox in two ways: you can download the Aurora, or you can download the .apk from the thread. Either way, you'll have to allow installation from unknown sources by going to settings > apps (which may vary by device; mine is under "security"), and checking "Unknown sources." Then, just download the .apk file, tap to launch it, and let the installation take over. Note that either of these versions can run independently of your existing Firefox installation, so you can run them both (or all three) side by side.
The differences between installing Aurora and the patched Fennec are minor but notable: Aurora can be checked for updates, so you'll always have the bleeding edge version of Firefox. The Fennec .apk won't update, so you'll always have version 26.0a1 unless you manually replace it.
The other difference is what I set out to look for in the first place: Aurora still uses the bounce-back effect, while the patched version of Fennec does not.
Keep in mind that these browsers are considered unstable, so you may experience problems, but in using Fennec for three days as my primary browser, I've yet to face a problem. Your mileage may vary.