1. The best options for delegating from websites to installed apps I've seen (via the long-press menu or by touching the Android when it appears in the URL bar).
2. Extensions. For me, browsing is practically uncivilized without Self-Destructing Cookies and there are lots of other useful ones.
3. The new "Open later" feature, where Firefox collects the URLs you click on, but doesn't load them until you switch to it. Among other things, it is a great way to collect links to look at from the Google Search app.
My only real annoyance with it are the occasional sites that make broken mobile browser assumptions so I end up spoofing Android Chrome or Mobile Safari. At least there's Phony, so the spoofing is pretty easy.