mozilla/addon-sdk — pull request #716 by Mossop (2013-01-08 00:43:23+00:00)
Title: Bug 719206 - Put our python libraries first in the path to override any system installed mozrunner

Maybe this is an easy solution, the problem is we stick our python libraries at the end of the search path so when we import mozrunner anything earlier on the system gets used instead. Putting our libraries at the start solves this for at least the once case I can reproduce