Which are the type of extensions that change so much about the browser that average users just won't use them.

When I discovered Classic Theme Restorer, Tab Mix Plus and similar, I was already a semi-pro user and I still found them intimidating.

There were a lot of checkboxes and they changed around a lot of things and I didn't yet know how to create a separate Firefox profile where I could've actually just wildly tried different options without the fear of something breaking irreversibly.