Want YouTube links automatically redirected to a random invidious instance? It is trivial to write a URL rewrite function in emacs and have it transform all links you click before they are opened in a browser, and the function can be as expressive as you want. In Firefox? You need a fully fledged web extension, signed by mozilla, with limited functionalities. And if you write one yourself, any iteration big or small requires a new Mozilla sign to work properly across browsing sessions.