--- a/testing/mozharness/configs/web_platform_tests/prod_config.py
+++ b/testing/mozharness/configs/web_platform_tests/prod_config.py
@@ -22,13 +22,13 @@ config = {
          "https://blobupload.elasticbeanstalk.com",
     ],
 
     "blob_uploader_auth_file" : os.path.join(os.getcwd(), "oauth.txt"),
 
     "download_minidump_stackwalk": True,
 
     # this would normally be in "exes", but "exes" is clobbered by remove_executables
-    "geckodriver": "%(abs_test_bin_dir)s/geckodriver",
+    "geckodriver": os.path.join("%(abs_test_bin_dir)s", "geckodriver"),
 
     "per_test_category": "web-platform",
 }
 

--- a/testing/mozharness/configs/web_platform_tests/prod_config_windows.py
+++ b/testing/mozharness/configs/web_platform_tests/prod_config_windows.py
@@ -23,17 +23,20 @@ config = {
     "exes": {
         'python': sys.executable,
         'hg': 'c:/mozilla-build/hg/hg',
     },
 
     "buildbot_json_path": "buildprops.json",
 
     "default_blob_upload_servers": [
-         "https://blobupload.elasticbeanstalk.com",
+        "https://blobupload.elasticbeanstalk.com",
     ],
 
-    "blob_uploader_auth_file" : os.path.join(os.getcwd(), "oauth.txt"),
+    "blob_uploader_auth_file": os.path.join(os.getcwd(), "oauth.txt"),
 
     "download_minidump_stackwalk": True,
 
+    # this would normally be in "exes", but "exes" is clobbered by remove_executables
+    "geckodriver": os.path.join("%(abs_test_bin_dir)s", "geckodriver.exe"),
+
     "per_test_category": "web-platform",
 }

--- a/testing/mozharness/configs/web_platform_tests/prod_config_windows_taskcluster.py
+++ b/testing/mozharness/configs/web_platform_tests/prod_config_windows_taskcluster.py
@@ -21,42 +21,45 @@ config = {
     ],
 
     "exes": {
         'python': sys.executable,
         'hg': os.path.join(os.environ['PROGRAMFILES'], 'Mercurial', 'hg')
     },
 
     "default_blob_upload_servers": [
-         "https://blobupload.elasticbeanstalk.com",
+        "https://blobupload.elasticbeanstalk.com",
     ],
 
     "run_cmd_checks_enabled": True,
     "preflight_run_cmd_suites": [
         {
             'name': 'disable_screen_saver',
             'cmd': ['xset', 's', 'off', 's', 'reset'],
             'architectures': ['32bit', '64bit'],
             'halt_on_failure': False,
             'enabled': False
         },
         {
             'name': 'run mouse & screen adjustment script',
             'cmd': [
                 sys.executable,
                 os.path.join(os.getcwd(),
-                    'mozharness', 'external_tools', 'mouse_and_screen_resolution.py'),
+                             'mozharness', 'external_tools', 'mouse_and_screen_resolution.py'),
                 '--configuration-file',
                 os.path.join(os.getcwd(),
-                    'mozharness', 'external_tools', 'machine-configuration.json')
+                             'mozharness', 'external_tools', 'machine-configuration.json')
             ],
             'architectures': ['32bit', '64bit'],
             'halt_on_failure': True,
             'enabled': True
         }
     ],
 
-    "blob_uploader_auth_file" : 'C:/builds/oauth.txt',
+    "blob_uploader_auth_file": 'C:/builds/oauth.txt',
 
     "download_minidump_stackwalk": True,
 
+    # this would normally be in "exes", but "exes" is clobbered by remove_executables
+    "geckodriver": os.path.join("%(abs_test_bin_dir)s", "geckodriver.exe"),
+
     "per_test_category": "web-platform",
 }