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.
On Android, I recommend the UntrackMe app. It basically does the same as LibRedirect. You can also use this hack to install desktop extensions like LibRedirect in Firefox Mobile, it requires Fennec Nightly (essentially the Firefox beta version) or Mull (hardened Firefox which is built from Fennec Nightly) though.