https://route66custom.com/frpfe@cynwoody.appspot.com.xpi
Come to find out, those xpi files sit in your firefox profile's extensions folder so anyone who has the addon installed, has the xpi file for installing it.
Your FF profile should be backed up on occasion. To see your profile(s), put this in for a url - about:profiles
Your profile folder holds extensions, settings, history, bookmarks, even currently open tabs.
More;
https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles
Chrome only allows installing extensions from the Chrome store now. The file extensions are also different. CRX for Chrome vs XPI for Firefox. Not sure what the file contents differences are.
Thank you!
Link did not work for me, but I placed it here for now. https://www.peacebyjesus.net/frpostfenhancer.xpi Do have any contact with Cynwoody, since I am only presuming permission.