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.
I have used LibRedirect for quite a good while now. It replaced Privacy Redirector, Teddit Redirect, and other addons together, and covers the largest swathe of web services amongst all the addons, is very customisable and the instance ping test feature is brilliant for checking dead and active instances.