With Mac OS X 10.12 you can use the current release and it isn't recommended to install older version and specially 32-bit Firefox on Mac using a version that supports a universal binary.

I don't know when they started offering only 64-bit and stopped with the universal builds. What reasons do you have for going back to 32-bit Firefox ?

Firefox 53.0 (released way back on April 19, 2017) dropped support for 32-bit macOS as it was 64-bit only from that point.

This question has been locked because the original author has deleted their account. While you can no longer post new replies, the existing content remains available for reference.