--- a/testing/marionette/harness/marionette_harness/tests/unit/test_navigation.py
+++ b/testing/marionette/harness/marionette_harness/tests/unit/test_navigation.py
@@ -491,21 +491,21 @@ class TestBackForwardNavigation(BaseNavi
         self.run_bfcache_test(test_pages)
 
     def test_image_to_image(self):
         test_pages = [
             {"url": self.marionette.absolute_url("black.png")},
             {"url": self.marionette.absolute_url("white.png")},
         ]
         self.run_bfcache_test(test_pages)
-      
+
     def test_image_urls(self):
         test_images = [
             {"url": self.marionette.absolute_url("black.png")},
-            {"url": self.marionette.absolute_url("white.png")},           
+            {"url": self.marionette.absolute_url("white.png")},
             {"url": inline_image(RED_PIXEL)},
             {"url": inline_image(BLACK_PIXEL)},
             {"url": self.marionette.absolute_url("black.png")},
         ]
         self.run_bfcache_test(test_images)
 
     @run_if_e10s("Requires e10s mode enabled")
     def test_remoteness_change(self):