Hope that they develop easy installer for existing devices (like CyanogenMod is planning). My Galaxy S2 would be possible target for Firefox OS, but current install system looks risky and too much work.
I ordered ZTE Open, but would like to use FFOS with better hardware also.
Jolla phone looks promising (with Android compatibility), maybe after pre-order stage when prices drop.
They should sell their phones also via Ebay or some other site for international market...like ZTE does.