This phone has a older ARMv6 type of cpu (a Qualcomm MSM7227T) when ARMv7 is required as to why the phone is not compatible.

The good news is that Mozilla is looking to try and get ARMv6 Firefox releases in future.

There are third-party ARMv6 builds of mobile Firefox that you can try at your own risk at http://forum.xda-developers.com/showthread.php?p=25855563

https://wiki.mozilla.org/Mobile/Platforms/Android#System_Requirements

These devices have ARMv6 processors and are not compatible with Firefox for Android. We are working on ARMv6 support: 

HTC ChaCha

Thank you

James,

We actually have official ARMv6 builds now available for download: http://nightly.mozilla.org (select the ARMv6 download option at the bottom under the Android category).

Thank you so very much..............

ojhaplus, one thing he did not mention (and is partially why I did not mention them) is that those builds are more bleeding edge at 17.0a1 development and the Nightly channel gets checkins pretty much each day and there a update each of those days.

If you do not mind being a Tester, then try the Nightly channel.