There's a core team (https://github.com/rust-lang/rust/wiki/Note-core-team) responsible for final decisions on the direction of the language and libraries. Proposed changes go through a public RFC process (https://github.com/rust-lang/rfcs#what-the-process-is), including those proposed by members of the core team -- which are frequently revised or even rejected as part of this process. See for example the path API RFC (https://github.com/rust-lang/rfcs/pull/474).

PRs can be reviewed by anyone from a large pool of reviewers. PRs that introduce new features etc. have to come after an RFC is approved, however.

The core team includes Huon Wilson, Yehuda Katz, and Steve Klabnik, none of whom work for Mozilla (though the latter two have done some contracting work). We hope to continue expanding to include other stakeholders.

EDIT: Steve tells me he's currently working as a "seasonal employee" at Mozilla for doing Rust docs, but it's a short term thing.