Because this version is no longer active, it is not available on the main Firefox homepage. You must access it through Mozilla's official archive servers:
Firefox ESR is a version of Firefox that receives updates for a longer period than the standard release. This makes it an attractive option for organizations, governments, and educational institutions that require a stable browser for their daily operations. ESR versions are typically supported for one year, with security updates and bug fixes applied regularly. firefox version 52.9. 0 esr download
: Firefox Setup 52.9.0esr.exe — Required for Windows XP and Vista. Because this version is no longer active, it
Firefox version 52.9. 0 ESR was the last supported release for Windows XP and Windows Vista. Mozilla Support firefox version 52.9. 0 esr download