From the github page it looks like external folks are submitting pull requests. It looks like they require external people to sign the CLA, but it doesn't look like it's a case of "good luck making any changes that help you but don't help FB" per your comment.
I've found the same as you - people are getting their PRs when needed. In the earlier days of the project, it may have been true that they were less accepting of any non-critical changes (as they were still getting the core together), but in my experience they're open and eager to get feedback from the public.
