cat: backend.TestManifestBackend.in: No such file or directory
Build configuration changed. Regenerating backend.
make: /home/hyperion/firefox/obj-x86_64-pc-linux-gnu/_virtualenvs/init/bin/python: Command not found
/home/hyperion/firefox/build/rebuild-backend.mk:24: recipe for target 'backend.TestManifestBackend' failed
make: *** [backend.TestManifestBackend] Error 127
Error running mach:

    ['test', 'testing/marionette/harness/marionette_harness/tests/unit/test_visibility.py']

The error occurred in code that was called by the mach command. This is either
a bug in the called code itself or in the way that mach is calling it.

You should consider filing a bug for this issue.

If filing a bug, please include the full output of mach, including this error
message.

The details of the failure are as follows:

Exception: Process executed with non-0 exit code 2: [u'/usr/bin/make', u'-f', u'/home/hyperion/firefox/build/rebuild-backend.mk', u'-j4', u'-s', u'backend.TestManifestBackend']

  File "/home/hyperion/firefox/testing/mach_commands.py", line 119, in test
    resolver = self._spawn(TestResolver)
  File "/home/hyperion/firefox/python/mozbuild/mozbuild/base.py", line 752, in _spawn
    topobjdir=self.topobjdir)
  File "/home/hyperion/firefox/testing/mozbase/moztest/moztest/resolve.py", line 508, in __init__
    self.topsrcdir, 'build', 'gen_test_backend.py'),
  File "/home/hyperion/firefox/python/mozbuild/mozbuild/base.py", line 680, in _run_make
    return fn(**params)
  File "/home/hyperion/firefox/python/mozbuild/mozbuild/base.py", line 735, in _run_command_in_objdir
    return self.run_process(cwd=self.topobjdir, **args)
  File "/home/hyperion/firefox/python/mach/mach/mixin/process.py", line 162, in run_process
    raise Exception('Process executed with non-0 exit code %d: %s' % (status, args))
hyperion@hyperion:~/firefox$