The mobile version of Firefox is dependent upon the processor being used. The LG Optimus One has an ARM 11 processor which uses the ARMv6 architecture. The mobile version of Firefox requires a processor that uses the ARMv7 architecture. There are experimental builds that '''may '''work on the LG Optimus One, for details see https://wiki.mozilla.org/Mobile/Platforms/Android in particular the part about the ARMv6 experimental builds.