will firefox work GT-S 6102 SAMSUNG GALAXY DUOS DEVICE ?Give answer by email please ...

Definitely!

You can download Firefox for Android at https://play.google.com/store/apps/details?id=org.mozilla.firefox or by going to the Play Store app on your phone and typing Firefox then downloading.

Hmm it is a little low on the hardware specs with only 384 MB RAM, a 833 MHz ARMv6 (and not v7) cpu, display resolution of 240 x 320. Basically the minimum specs on most things.

https://support.mozilla.org/en-US/kb/will-firefox-work-my-mobile-device