I find its UI better on my 7 inch tablet (those tabs in Chrome are small and annoying and I also prefer Firefox's UI when doing searches). It also has add-ons and for example I use AdBlock Plus (websites on your mobile full of ads are unusable), HTTPS Everywhere (especially important for mobile devices that connect to public Wifis) and LastPass.

It also has a Reader Mode that strips the annoying styling off an article, much like Readability or Pocket. You can also save articles for later reading. Feature is still young, but it's been working well for me.

It also inherits the Awesome Bar from the desktop version. It does a very good job at suggesting previous links from your history. This saves you from doing searches on Google, which many times is like searching for a needle in a haystack.

It's also a platform for apps, apps that get published in the Firefox Marketplace and that can work in Firefox OS as well as on Android (and more recently on your desktop). Much like Chrome for desktop does, but it works on your mobile. Still young, doesn't have many apps, but it's been growing and improving and the whole thing is based on web standards or APIs that Mozilla is pushing for standardization.

Try it out, you might like it. And let me tell you, once you become hooked to one of its add-ons, you won't be able to switch back to Chrome anymore ;-)