Firefox OS is the way to go!

[erotavlas]

At the moment you have to follow this procedure https://developer.mozilla.org/en-US/Firefox_OS/Preparing_for_your_first_B2G_build
I know that it is a little bit complicated for a person that is not a developer.
However, you need Linux or Mac OS X.
The basic steps are
git clone git://github.com/mozilla-b2g/B2G.git && cd B2G // cloning the repository ./config.sh fairphone2 // configuring the build cd B2G ./build.sh -j2 // building 30-60 minutes ./flash.sh // installing the build into the device
Several developers said that they already built the system https://bugzilla.mozilla.org/show_bug.cgi?id=1139642. I’m building it and I will provide a link for download so you can follow only the final step https://developer.mozilla.org/en-US/docs/Mozilla/Firefox_OS/Installing_on_a_mobile_device

[paulakreuzer]

I just installed the Firefox OS launcher - which by the way works a lot better on FP2 than on FP1 - and now I can’t wait to get Firefox OS running on my FP2.

[uBkUN27v]

Oops, then I have been falsely informed. I apologize for the misleading news.