The purpose of this extension is exactly what you complain about: to jump back and forward when you swipe horizontally. So I'm not sure what you were expecting when you installed it. Did you know that you can adjust the sensitivity of the extention in its settings page so you can tune how much swipe triggers the jump, so that you can still be able to scroll horizontally on pages?

Moreover, no extension at all works on Firefox' about pages, like about:home, as well as on any site in the firefox.com, mozilla.org and mozilla.com domains. This is for security policy. You can unblock this security restriction at your own risk on these domains by opening a new tab, insert in the URL bar about:config and search for the following preference, and put an empty value inside: "extensions.webextensions.restrictedDomains". On about:* pages, however, don't expect any other extension at all to work