Tried the extension on both Firefox Beta(V60) and Firefox Nightly(V61.a01) and did not function correctly on either. When user agent is set to google chrome It will redirect after it has fully loaded the amp page and you manually press refresh. Defeating the purpose of the extension.
I love the idea of this addon but it doesn't work on Fennec/Firefox Mobile. If I Google search for an article the first result will be an AMP result and will not redirect off of Google's page. If I knew what other websites this addon was developed for, I could test those as well if you want.