This is a plugin I found recently and really enjoy. It gives you the opportunity to redirect several webpages to alternatives. For example Youtube to FreeTube or Piped. If I search for youtube in Firefox, FreeTube automatically opens and shows me my feed. I like it, I use it, I can recommend it.
It’s not letting me add it to mobile. Any idea why?
I can’t talk about the official Firefox client on mobile, but i use Iceraven on Android and i can add “Privacy Redirect” which does essentially the same, but for less services
no.