--- a/testing/mozbase/mozprocess/mozprocess/processhandler.py
+++ b/testing/mozbase/mozprocess/mozprocess/processhandler.py
@@ -7,19 +7,21 @@ from __future__ import absolute_import, 
 import errno
 import os
 import signal
 import subprocess
 import sys
 import threading
 import time
 import traceback
+
 from Queue import Queue, Empty
 from datetime import datetime
 
+
 __all__ = ['ProcessHandlerMixin', 'ProcessHandler', 'LogOutput',
            'StoreOutput', 'StreamOutput']
 
 # Set the MOZPROCESS_DEBUG environment variable to 1 to see some debugging output
 MOZPROCESS_DEBUG = os.getenv("MOZPROCESS_DEBUG")
 
 # We dont use mozinfo because it is expensive to import, see bug 933558.
 isWin = os.name == "nt"
@@ -867,16 +869,47 @@ falling back to not using job objects fo
         print("MOZPROCESS WARNING: ProcessHandler.waitForFinish() is deprecated, "
               "use ProcessHandler.wait() instead", file=sys.stderr)
         return self.wait(timeout=timeout)
 
     @property
     def pid(self):
         return self.proc.pid
 
+    @staticmethod
+    def pid_exists(pid):
+        if pid < 0:
+            return False
+
+        if isWin:
+            try:
+                process = winprocess.OpenProcess(
+                    winprocess.PROCESS_QUERY_INFORMATION | winprocess.PROCESS_VM_READ, False, pid)
+                return winprocess.GetExitCodeProcess(process) == winprocess.STILL_ACTIVE
+
+            except WindowsError as e:
+                # no such process
+                if e.winerror == winprocess.ERROR_INVALID_PARAMETER:
+                    return False
+
+                # access denied
+                if e.winerror == winprocess.ERROR_ACCESS_DENIED:
+                    return True
+
+                # re-raise for any other type of exception
+                raise
+
+        elif isPosix:
+            try:
+                os.kill(pid, 0)
+            except OSError as e:
+                return e.errno == errno.EPERM
+            else:
+                return True
+
     @classmethod
     def _getpgid(cls, pid):
         try:
             return os.getpgid(pid)
         except OSError as e:
             # Do not raise for "No such process"
             if e.errno != errno.ESRCH:
                 raise

--- a/testing/mozbase/mozprocess/mozprocess/winprocess.py
+++ b/testing/mozbase/mozprocess/mozprocess/winprocess.py
@@ -160,17 +160,22 @@ class EnvironmentBlock:
                 if isinstance(v, bytes):
                     v = v.decode(fs_encoding, 'replace')
                 values.append("{}={}".format(k, v))
             values.append("")
             self._as_parameter_ = LPCWSTR("\0".join(values))
 
 
 # Error Messages we need to watch for go here
-# See: http://msdn.microsoft.com/en-us/library/ms681388%28v=vs.85%29.aspx
+
+# https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx (0 - 499)
+ERROR_ACCESS_DENIED = 5
+ERROR_INVALID_PARAMETER = 87
+
+# http://msdn.microsoft.com/en-us/library/ms681388%28v=vs.85%29.aspx (500 - 999)
 ERROR_ABANDONED_WAIT_0 = 735
 
 # GetLastError()
 GetLastErrorProto = WINFUNCTYPE(DWORD)  # Return Type
 GetLastErrorFlags = ()
 GetLastError = GetLastErrorProto(("GetLastError", windll.kernel32), GetLastErrorFlags)
 
 # CreateProcess()
@@ -246,16 +251,45 @@ JOB_OBJECT_MSG_ABNORMAL_EXIT_PROCESS = 8
 JOB_OBJECT_MSG_PROCESS_MEMORY_LIMIT = 9
 JOB_OBJECT_MSG_JOB_MEMORY_LIMIT = 10
 
 # See winbase.h
 DEBUG_ONLY_THIS_PROCESS = 0x00000002
 DEBUG_PROCESS = 0x00000001
 DETACHED_PROCESS = 0x00000008
 
+# OpenProcess -
+# https://msdn.microsoft.com/en-us/library/windows/desktop/ms684320(v=vs.85).aspx
+PROCESS_QUERY_INFORMATION = 0x0400
+PROCESS_VM_READ = 0x0010
+
+OpenProcessProto = WINFUNCTYPE(
+    HANDLE,  # Return type
+    DWORD,   # dwDesiredAccess
+    BOOL,    # bInheritHandle
+    DWORD,   # dwProcessId
+)
+
+OpenProcessFlags = (
+    (1, "dwDesiredAccess", 0),
+    (1, "bInheritHandle", False),
+    (1, "dwProcessId", 0),
+)
+
+
+def ErrCheckOpenProcess(result, func, args):
+    ErrCheckBool(result, func, args)
+
+    return AutoHANDLE(result)
+
+
+OpenProcess = OpenProcessProto(("OpenProcess", windll.kernel32),
+                               OpenProcessFlags)
+OpenProcess.errcheck = ErrCheckOpenProcess
+
 # GetQueuedCompletionPortStatus -
 # http://msdn.microsoft.com/en-us/library/aa364986%28v=vs.85%29.aspx
 GetQueuedCompletionStatusProto = WINFUNCTYPE(BOOL,         # Return Type
                                              HANDLE,       # Completion Port
                                              LPDWORD,      # Msg ID
                                              LPULONG,      # Completion Key
                                              # PID Returned from the call (may be null)
                                              LPULONG,

--- a/testing/mozbase/mozprocess/tests/proctest.py
+++ b/testing/mozbase/mozprocess/tests/proctest.py
@@ -1,14 +1,16 @@
 from __future__ import absolute_import
 
 import os
 import sys
 import unittest
-import psutil
+
+from mozprocess import ProcessHandler
+
 
 here = os.path.dirname(os.path.abspath(__file__))
 
 
 class ProcTest(unittest.TestCase):
 
     @classmethod
     def setUpClass(cls):
@@ -22,17 +24,17 @@ class ProcTest(unittest.TestCase):
             proc -- the processhandler instance
             isalive -- Use True to indicate we pass if the process exists; however, by default
                        the test will pass if the process does not exist (isalive == False)
             expectedfail -- Defaults to [], used to indicate a list of fields
                             that are expected to fail
         """
         returncode = proc.proc.returncode
         didtimeout = proc.didTimeout
-        detected = psutil.pid_exists(proc.pid)
+        detected = ProcessHandler.pid_exists(proc.pid)
         output = ''
         # ProcessHandler has output when store_output is set to True in the constructor
         # (this is the default)
         if getattr(proc, 'output'):
             output = proc.output
 
         if 'returncode' in expectedfail:
             self.assertTrue(returncode, "Detected an unexpected return code of: %s" % returncode)