diff --git a/testing/mozbase/mozprocess/mozprocess/processhandler.py b/testing/mozbase/mozprocess/mozprocess/processhandler.py
index 77ac14c74857..ee2a6eab50a6 100644
--- a/testing/mozbase/mozprocess/mozprocess/processhandler.py
+++ b/testing/mozbase/mozprocess/mozprocess/processhandler.py
@@ -721,9 +721,7 @@ falling back to not using job objects for managing child processes""", file=sys.
         self.keywordargs = kwargs
         self.read_buffer = ''
 
-        # XXX Bug 1585702 - Setting env is broken on Windows + Python 3. In the
-        # meantime let's at least make sure we don't set it in the default case.
-        if env is None and not (six.PY3 and isWin):
+        if env is None:
             env = os.environ.copy()
         self.env = env
 
diff --git a/testing/mozbase/mozprocess/mozprocess/winprocess.py b/testing/mozbase/mozprocess/mozprocess/winprocess.py
index 6b965a318b1e..446578ca0b4b 100644
--- a/testing/mozbase/mozprocess/mozprocess/winprocess.py
+++ b/testing/mozbase/mozprocess/mozprocess/winprocess.py
@@ -38,7 +38,18 @@ from __future__ import absolute_import, unicode_literals, print_function
 
 import subprocess
 import sys
-from ctypes import c_void_p, POINTER, sizeof, Structure, windll, WinError, WINFUNCTYPE, c_ulong
+from ctypes import (
+    cast,
+    create_unicode_buffer,
+    c_ulong,
+    c_void_p,
+    POINTER,
+    sizeof,
+    Structure,
+    windll,
+    WinError,
+    WINFUNCTYPE,
+)
 from ctypes.wintypes import BOOL, BYTE, DWORD, HANDLE, LPCWSTR, LPWSTR, UINT, WORD
 
 from .qijo import QueryInformationJobObject
@@ -163,8 +174,13 @@ 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))
+
+            # The lpEnvironment parameter of the 'CreateProcess' function expects a series
+            # of null terminated strings followed by a final null terminator. We write this
+            # value to a buffer and then cast it to LPCWSTR to avoid a Python ctypes bug
+            # that probihits embedded null characters (https://bugs.python.org/issue32745).
+            values = create_unicode_buffer("\0".join(values) + "\0")
+            self._as_parameter_ = cast(values, LPCWSTR)
 
 
 # Error Messages we need to watch for go here
diff --git a/testing/mozbase/mozprocess/tests/manifest.ini b/testing/mozbase/mozprocess/tests/manifest.ini
index 119910f029ac..ec1dcf2cff6a 100644
--- a/testing/mozbase/mozprocess/tests/manifest.ini
+++ b/testing/mozbase/mozprocess/tests/manifest.ini
@@ -1,7 +1,5 @@
 [DEFAULT]
 subsuite = mozbase
-# Python bug https://bugs.python.org/issue32745
-skip-if = python == 3 && os == "win"  # Bug 1428713 for more info
 [test_detached.py]
 skip-if = os == "win"  # Bug 1493796
 [test_kill.py]