Thanks for adding the link, I grabbed the installer from
/pub/firefox/releases/102.15.1esr/win64/en-US/Firefox Setup 102.15.1esr.msi
It installed without warning over my Firefox 122. It did prompt me to save my profile.
Afterward, I learned about the Profile Manager, and ran "firefox -P" to see I have two profiles,
"default -esr" and just "default".
However, somewhere along the way Firefox ESR upgraded to 115.7.0esr.
It looks like I have to unset "Automatically install updates" in General Preferences right after it first starts.
Next, I'll try to install Firefox 122 over the ESR, and then try again.
As you can tell, I am new to the Firefox platform.