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 you can enable “share”/“open in external app” and send the link to piped or newpipe or whatever your preferred app is; that’s how I do it