I agree with robert3353 that this add-on is the only reason I use Firefox at all. Here is how I got the add-on to work for now:

Note that I am using the add-on Classic Theme Restorer. I am also running Firefox ESR 32-bit as I attempt to hold on to features. You can get the ESR version at https://www.mozilla.org/en-US/firefox/organizations/all/

You can find version 2.4.8 at https://addons.mozilla.org/en-US/firefox/addon/forecastfox-fix-version/versions

Find Forecastfox under Tools / Extensions or simply at about:addons

Click on More.

Find Automatic Updates near the bottom of the page.

Click on Off.