Firefox Extended Support Release (ESR) is an official version of Firefox developed for large organizations (Firefox for enterprise) like universities and businesses that need to set up and maintain Firefox on a large scale. Firefox ESR does not come with the latest features but it has the latest security and stability fixes.
All US English Firefox browser links:
Firefox Release Calendar
FTP link to software releases
Check HASH Value of Software Download: 102.1.0esr in this case, subject to frequent version change note