The list of supported mobile devices is at https://support.mozilla.org/en-US/kb/will-firefox-work-my-mobile-device. Some phones not on that list either haven't been tested, or don't have enough hardware capability to run Firefox.

Sorry but your Samsung Galaxy Y does not support the mobile Firefox as it is using the older ARMv6 type of cpu. The RAM is also low at 290MB when 512+ is recommended. It was the cheapest smartphone available in the Galaxy series to-date when released so it is no surprise for it have the ARMv6 and low RAM amount.

This incompatibility is final or there is the possibility of Firefox be adapted for this hardware?

We are looking to support the ARMv6 market eventually as they are more than half the market. There are unoffical ARMv6 builds at http://forum.xda-developers.com/showthread.php?t=1643785 Mozilla makes no claims about their stability or reliability.

I used samsung galaxy pop gt s5570 mobile. but it not support mozilla firefox.. i want to use mozilla firefox... plz upgrade this application & allow to use samsung galaxy pop..

http://www.gsmarena.com/samsung_galaxy_mini_s5570-3725.php

Sorry, another ARMv6 processor and only 348 MB of RAM.

^which has the rather common Qualcomm MSM7227 cpu which is ARMv6.

Mozilla is progressing further and further along into finally having releases for the ARMv6.

Not to say the builds will work well on a ARMv6 devices with under 512Mb ram and has a slow cpu.