--- a/testing/marionette/harness/marionette_harness/tests/unit/test_window_maximize.py
+++ b/testing/marionette/harness/marionette_harness/tests/unit/test_window_maximize.py
@@ -33,24 +33,25 @@ class TestWindowMaximize(MarionetteTestC
     def assert_window_maximized(self, actual, delta=None):
         if self.marionette.session_capabilities["platformName"] == "windows_nt":
             delta = 16
         else:
             delta = 8
 
         self.assertGreater(
             actual["width"], self.max["width"] - delta,
-            msg="Window width is not within {} px of availWidth: "
-                "current width {} and max width {}"
-                .format(delta, actual["width"], self.max["width"] - delta))
-        self.assertGreater(
+            msg="Window width is not within {delta} px of availWidth: "
+                "current width {expected} should be greater than max width {max}"
+                .format(delta=delta, expected=actual["width"], max=self.max["width"] - delta))
+        self.assertAlmostEqual(
             actual["height"], self.max["height"],
+            delta=delta,
             msg="Window height is not within {} px of availHeight, "
                 "current height {} and max height {}"
-                .format(delta, actual["height"], self.max["height"] - delta))
+                .format(delta, actual["height"], self.max["height"]))
 
     def assert_window_restored(self, actual):
         self.assertEqual(self.original_size["width"], actual["width"])
         self.assertEqual(self.original_size["height"], actual["height"])
 
     def assert_window_rect(self, rect):
         self.assertIn("width", rect)
         self.assertIn("height", rect)

--- a/testing/marionette/harness/marionette_harness/tests/unit/test_window_rect.py
+++ b/testing/marionette/harness/marionette_harness/tests/unit/test_window_rect.py
@@ -116,18 +116,18 @@ class TestSize(MarionetteTestCase):
 
         # WebDriver spec says a resize cannot result in window being
         # maximised, an error is returned if that is the case; therefore if
         # the window is maximised at the start of this test, returning to
         # the original size via set_window_size size will result in error;
         # so reset to original size minus 1 pixel width
         start_size = self.marionette.window_size
         if start_size["width"] == self.max["width"] and start_size["height"] == self.max["height"]:
-            start_size["width"] -= 1
-            start_size["height"] -= 1
+            start_size["width"] -= 10
+            start_size["height"] -= 10
         self.marionette.set_window_size(start_size["width"], start_size["height"])
 
         self.original_size = self.marionette.window_size
 
     def tearDown(self):
         self.marionette.set_window_size(
             self.original_size["width"], self.original_size["height"])
         is_fullscreen = self.marionette.execute_script("return document.fullscreenElement;", sandbox=None)