I have recently submitted MozillaFirefox-theme-oxygen to mozilla:Factory. Wolfgang Rosenauer has been very helpful with lots of feedback. I really appreciate his effort to guide me through the process of submitting a package to factory.
This package contains the Oxygen icon set for Firefox. The author is Harald Sitter and it is published under the MPL, CC-by-SA or LGPL. So far, no security issues are known.