Firefox Relay is meant for this. It can create a new mask in a single click, and it will forward emails to your actual address as long as you have it enabled. I’m not sure if you can send emails, but that’s rarely needed.
I’m not sure how (or really, if) they keep their domain (mozmail I think?) from being blocked by websites as a source of spam.
Sure, but they are always worse because of the exact reason they decided to create their own wiki, such as Conservapedia
You may peruse this list of online encyclopedias.