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.
LibReddit does work?
I use it with LibRedirect, sometimes they block instances, you can switch to the next one in the addon
From their github page: