[ubuntu] Firefox can't stream videos?!

My Firefox browser is no longer capable of streaming videos on websites like Netflix, Udemy, or Crunchyroll!

3 days ago, I wiped my Windows OS from my laptop and switched to Ubuntu for the first time ever. I love it so far and there’s no going back! But my understanding of Linux is still very basic, and I don’t know how to solve this problem with streaming videos. The ONLY place I can watch videos on the browser is on YouTube for some reason. I googled for solutions, but the only thing I found was to install some codecs (not sure what those are yet) with

and when I do that, it brings up some Microsoft agreement that I can’t move forward with because nothing lets me proceed with the modal! Any advice here??