hi, firefox for android also supports 2.3 - however it needs certain minimal hardware requirements (like a certain amount of RAM and type of cpu architecture). more details about that are available at: Will Firefox work on my mobile device?

Yes as Phillipp mentioned Firefox will run on on Android 2.3. However your device runs a CPU that is unsupported.

Yes the old LG p690 phone from 2011 has a ARMv6 type of cpu and not say ARMv7 or better.

Android 2.3 has been a minimum since mobile Firefox 31.0 Release and support for the old ARMv6 was dropped then.