For those interested in learning about a variety of topics related to Desktop Firefox, we have some good resources on MDN that might be of help, especially if you are interested in:
- Reporting Bugs
- Triaging Bugs
- Writing Test Cases
- Creating Automation
Please let us know if you have any suggestions for improving the documents, or if you have any questions in general.
Of course, there is lots of other content that pertains to other products as well, including Firefox OS, Firefox for Android and Web QA. And a good read if you have time, since Gecko is shared across all Firefox platforms: https://wiki.mozilla.org/Gecko:Overview