Technically, you can enable it anywhere by using Redirector to prepend about:reader?url= to the URL, with a sort of white/blacklisting system using Regex. It may or may not be able to show a useful content summary, of course. There is a pretty accurate algorithm built into Firefox that evaluates if it does, and shows or hides the address bar button accordingly. Maybe an add-on can leech of the result of this algorithm?
I use this add-on. It doesn’t automatically turn on for every website but you get to choose which domains it works for and which domains it doesn’t.
Technically, you can enable it anywhere by using Redirector to prepend
about:reader?url=to the URL, with a sort of white/blacklisting system using Regex. It may or may not be able to show a useful content summary, of course. There is a pretty accurate algorithm built into Firefox that evaluates if it does, and shows or hides the address bar button accordingly. Maybe an add-on can leech of the result of this algorithm?