Which has an "easier" codebase for someone beginning as an open source contributor, Chromium or Firefox?

Ive done chrome extensions before. I was originally going to write one for Firefox as thatsy go-to browser but found that I couldn't understand the documentation and decided to jump shit to chrome

I don't really understand your question here, nor do I perceive your interests.

Everyone has a different perception of code and how easy it is to "learn" its purpose and contribute to it, so the question of what codebase "is easier" for us is pretty much useless to you. Generally someone would choose the codebase he/she likes more.

Furthermore did you not specify your experiences with anything. How are we supposed to recommend you a codebase if we don't even know what you (could) do?

Contributing to an open-source project is nothing you just do, you have to learn it first, and I think neither of those projects are even close to an "beginner friendly contribution project"

I would really like to provide better help to you, but since you haven't specified anything other than the projects in interest, I'm afraid I cannot provide any better help than this comment.

Just read the code and see which one is easier to understand 😄

Join chromium.
I have been doing stuff on the chromium os project for a bit. It's quite nice and their custom tools are easy to use.

They also have a custom bug report system that's pretty nice.

If you make enough pull requests, you can get an @chromium.org email too.

But you should check out chromium.org to get started.