Running: $ mach test devtools/client/webaudioeditor/test/browser_wa_destroy-node-01.js After instrumenting testing/mochitest/runtests.py as follow: > try: > print "try marionette 1." > from marionette import Marionette > print "try marionette 2." > from marionette_driver.addons import Addons > print "try marionette 3." > except ImportError as err: > # Marionette not needed nor supported on android > print "try marionette :(. (%s)" % str(err) > Marionette = None I get the following log: > try marionette 1. > try marionette :(. (No module named pkg_resources) Listing the paths in the sys.path, only show path to the source directory, the python installation path and the build directory: > […] > /home/nicolas/mozilla/oom-repo > /nix/store/kvj2h1fn25ksjn75iivkqjx8jdslr7a6-python-2.7.10/lib/python2.7/site-packages > /nix/store/kvj2h1fn25ksjn75iivkqjx8jdslr7a6-python-2.7.10/lib/python27.zip > /nix/store/kvj2h1fn25ksjn75iivkqjx8jdslr7a6-python-2.7.10/lib/python2.7 > /nix/store/kvj2h1fn25ksjn75iivkqjx8jdslr7a6-python-2.7.10/lib/python2.7/plat-linux2 > /nix/store/kvj2h1fn25ksjn75iivkqjx8jdslr7a6-python-2.7.10/lib/python2.7/lib-tk > /nix/store/kvj2h1fn25ksjn75iivkqjx8jdslr7a6-python-2.7.10/lib/python2.7/lib-old > /nix/store/kvj2h1fn25ksjn75iivkqjx8jdslr7a6-python-2.7.10/lib/python2.7/lib-dynload > /home/nicolas/mozilla/_build/firefox/bugzil.la/1273955/commit/x64/gcc48/dbg/build This list does not contain any path to setuptools install directory. To work-around this issue, and make this python script work. I had to add > sys.path.append("/nix/store/fp[…]72-python2.7-setuptools-18.0.1/lib/python2.7/site-packages/setuptools-18.0.1-py2.7.egg") in the runtests.py file.