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.
How fo you install it on there? I was under the impression the the Chromecast didn’t install anything, but served web-based applications housed on the external servers.