First of all the phone needs to have Android 2.0 or newer. Firefox will not appear in the Market for most phones with incompatible hardware. Without knowing what phone it is exactly, it would be hard to tell you whether it is compatible with recent mobile Firefox or not. The current mobile Firefox release is only support the ARMv7 as the ones that use a ARMv6 (part of ARM11 family) will not work. https://wiki.mozilla.org/Mobile/Platforms/Android#System_Requirements If it does use a ARMv6 then you can try the experimental nightlies. https://wiki.mozilla.org/Mobile/Platforms/Android#ARMv6_.28experimental.29