Mozilla Foundation always proves that it has some of the most talented engineers even if it is a no-profit organization. Their latest work is called Firefox Australis, featuring an updated visual design, streamlined tab strip, updated Firefox menu and improved customization.
Australis will land in Firefox stable channel in the few next months. It is a new version of Firefox, not a new product.
You can get the binaries from nightly.mozilla.org.
I don’t have lots of Firefox extensions, but what I had, it was compatible with Australis.
Firefox OS Availability
If you are interested to buy the low-cost HTML5 smartphones, you can re-check at mozilla.org/en-US/firefox/os/ since Mozilla is expanding the network of their carriers in more countries.