I went fishing for a Firefox plugin that would redirect me from YouTube to an invidious instance and ran across this:
https://github.com/SimonBrazell/privacy-redirect
A web extension that redirects Twitter, YouTube, Instagram, Google Maps, Reddit, Google Search, & Google Translate requests to privacy friendly alternative frontends for those sites - Nitter, Invidious, FreeTube, Bibliogram, OpenStreetMap, SimplyTranslate & Private Search Engines like DuckDuckGo and Startpage.
!
So now I'm back to looking for a simple plugin for invidious, with public source code.
@mikeburns thanks! manual configuration is actually a plus for something like this.
@edsu I use this plugin but unfortunately I have to manually configure it:
https://einaregilsson.com/redirector/