For users of legacy hardware or specialized software, downloading or the 52 ESR version is often a necessity rather than a choice. These versions represent a specific era of web browsing before Mozilla transitioned to the "Quantum" engine, which removed support for legacy NPAPI plugins and older operating systems. Why Users Download Firefox 12–51 and 52 ESR

The Transition Era: Firefox 12 to 51 and the Legacy of 52 ESR

The Internet Archive (archive.org) often hosts older versions of Firefox. You can search for the specific version you need and download it from there.