Hi
Thank you for your feedback.
About:config is not a feature that most people will use and it can make your browser seriously unstable. If you are wanting to make changes to test various things, I recommend Beta or Nightly. I have been using the Nightly version as my main browser for over a year with very few issues and Beta is even more stable than that.
We hope to include support for more add-ons with future updates. However, the team is evaluating how to do this in a way that avoids the security and compatibility issues we had with previous versions of Firefox.
You can follow the work on View Source at https://github.com/mozilla-mobile/fenix/issues/3972 and Save to .pdf at https://github.com/mozilla-mobile/fenix/issues/3709