A review is required before code is added to Mozilla's repository. In addition, contrary to what you might have seen in other open source projects, code is not pushed directly to the repository. Instead, once the code is approved by reviewers, they will request the code to be landed on the repository.
All this can be done somehow manually, but we have infrastructure in place to help us with reviews and landing code.
The following sections will guide you towards getting your code reviewed and landed in the repository. Start by setting up.