mozilla@ubuntu:~$ mozmill -b /home/mozilla/firefox4/
Traceback (most recent call last):
  File "/usr/local/bin/mozmill", line 9, in <module>
    load_entry_point('mozmill==1.5.4b6', 'console_scripts', 'mozmill')()
  File "/usr/local/lib/python2.6/dist-packages/mozmill/__init__.py", line 847, in cli
    CLI().run()
  File "/usr/local/lib/python2.6/dist-packages/mozmill/__init__.py", line 789, in run
    self.mozmill.start(runner=runner, profile=runner.profile)
  File "/usr/local/lib/python2.6/dist-packages/mozmill/__init__.py", line 230, in start
    self.runner.start()
  File "/usr/local/lib/python2.6/dist-packages/mozrunner/__init__.py", line 502, in start
    self.process_handler = run_command(self.command+self.cmdargs, self.env, **self.kp_kwargs)
  File "/usr/local/lib/python2.6/dist-packages/mozrunner/__init__.py", line 90, in run_command
    env=env, **killable_kwargs)
  File "/usr/lib/python2.6/subprocess.py", line 623, in __init__
    errread, errwrite)
  File "/usr/lib/python2.6/subprocess.py", line 1141, in _execute_child
    raise child_exception
OSError: [Errno 13] Permission denied