Rated 4 out of 5 stars
Thank You Metal321.
To change the maxVersion still works with FF 43, but will not work with FF 44.
The real problem is that this add-on is not signed. According to timeline of the Add-ons/Extension signing Mozilla-wiki page:
Firefox 40-42: Firefox warns about signatures but doesn't enforce them.
Firefox 43: Firefox will have a preference that allows signature enforcement to be disabled (xpinstall.signatures.required in about:config).
Firefox 44: Release and Beta versions of Firefox WILL NOT ALLOW UNSIGNED EXTENSIONS TO BE INSTALLED, WITH NO OVERRIDE.