diff --git a/testing/web-platform/tests/infrastructure/metadata/infrastructure/testdriver/click_iframe_crossorigin.sub.html.ini b/testing/web-platform/tests/infrastructure/metadata/infrastructure/testdriver/click_iframe_crossorigin.sub.html.ini
new file mode 100644
index 000000000000..10e24dd773ff
--- /dev/null
+++ b/testing/web-platform/tests/infrastructure/metadata/infrastructure/testdriver/click_iframe_crossorigin.sub.html.ini
@@ -0,0 +1,4 @@
+[click_iframe_crossorigin.sub.html]
+  [TestDriver click on a document in an iframe]
+    expected:
+      if os == "mac" and product == "chrome": [PASS, FAIL]  # https://github.com/web-platform-tests/wpt/issues/26295
diff --git a/testing/web-platform/tests/tools/ci/tests/test_pr_preview.py b/testing/web-platform/tests/tools/ci/tests/test_pr_preview.py
index 13aef5086631..ed6310c1ea12 100644
--- a/testing/web-platform/tests/tools/ci/tests/test_pr_preview.py
+++ b/testing/web-platform/tests/tools/ci/tests/test_pr_preview.py
@@ -10,6 +10,7 @@ import os
 import shutil
 import stat
 import subprocess
+import sys
 import tempfile
 import threading
 
@@ -171,6 +172,11 @@ def temp_repo():
 
     try:
         subprocess.check_call(['git', 'init'], cwd=directory)
+        # Explicitly create the default branch.
+        subprocess.check_call(
+            ['git', 'checkout', '-b', 'master'],
+            cwd=directory
+        )
         subprocess.check_call(
             ['git', 'config', 'user.name', 'example'],
             cwd=directory
@@ -220,7 +226,7 @@ def synchronize(expected_traffic, refs={}):
 
         child = subprocess.Popen(
             [
-                'python',
+                sys.executable,
                 subject,
                 '--host',
                 'http://{}:{}'.format(test_host, test_port),
@@ -267,7 +273,7 @@ def detect(event, expected_github_traffic, expected_preview_traffic):
 
         child = subprocess.Popen(
             [
-                'python',
+                sys.executable,
                 subject,
                 '--host',
                 'http://{}:{}'.format(test_host, github_port),
diff --git a/testing/web-platform/tests/tools/wpt/tests/test_wpt.py b/testing/web-platform/tests/tools/wpt/tests/test_wpt.py
index 02b611e378b8..74246fafdd77 100644
--- a/testing/web-platform/tests/tools/wpt/tests/test_wpt.py
+++ b/testing/web-platform/tests/tools/wpt/tests/test_wpt.py
@@ -170,15 +170,14 @@ def test_run_zero_tests():
         pytest.skip("port 8000 already in use")
 
     with pytest.raises(SystemExit) as excinfo:
-        wpt.main(argv=["run", "--yes", "--no-pause", "--binary-arg", "headless",
-                       "--channel", "dev", "chrome",
-                       "/non-existent-dir/non-existent-file.html"])
+        wpt.main(argv=["run", "--yes", "--no-pause", "--channel", "dev",
+                       "chrome", "/non-existent-dir/non-existent-file.html"])
     assert excinfo.value.code != 0
 
     with pytest.raises(SystemExit) as excinfo:
-        wpt.main(argv=["run", "--yes", "--no-pause", "--binary-arg", "headless",
-                       "--no-fail-on-unexpected", "--channel", "dev",
-                       "chrome", "/non-existent-dir/non-existent-file.html"])
+        wpt.main(argv=["run", "--yes", "--no-pause", "--no-fail-on-unexpected",
+                       "--channel", "dev", "chrome",
+                       "/non-existent-dir/non-existent-file.html"])
     assert excinfo.value.code != 0
 
 
@@ -196,14 +195,13 @@ def test_run_failing_test():
     assert os.path.isfile("../../%s" % failing_test)
 
     with pytest.raises(SystemExit) as excinfo:
-        wpt.main(argv=["run", "--yes", "--no-pause", "--binary-arg", "headless",
-                       "--channel", "dev", "chrome", failing_test])
+        wpt.main(argv=["run", "--yes", "--no-pause", "--channel", "dev",
+                       "chrome", failing_test])
     assert excinfo.value.code != 0
 
     with pytest.raises(SystemExit) as excinfo:
-        wpt.main(argv=["run", "--yes", "--no-pause", "--binary-arg", "headless",
-                       "--no-fail-on-unexpected", "--channel", "dev",
-                       "chrome", failing_test])
+        wpt.main(argv=["run", "--yes", "--no-pause", "--no-fail-on-unexpected",
+                       "--channel", "dev", "chrome", failing_test])
     assert excinfo.value.code == 0
 
 
@@ -227,15 +225,15 @@ def test_run_verify_unstable(temp_test):
     """)
 
     with pytest.raises(SystemExit) as excinfo:
-        wpt.main(argv=["run", "--yes", "--verify", "--binary-arg", "headless",
-                       "--channel", "dev", "chrome", unstable_test])
+        wpt.main(argv=["run", "--yes", "--verify", "--channel", "dev",
+                       "chrome", unstable_test])
     assert excinfo.value.code != 0
 
     stable_test = temp_test("test(function() {}, 'my test');")
 
     with pytest.raises(SystemExit) as excinfo:
-        wpt.main(argv=["run", "--yes", "--verify", "--binary-arg", "headless",
-                       "--channel", "dev", "chrome", stable_test])
+        wpt.main(argv=["run", "--yes", "--verify", "--channel", "dev",
+                       "chrome", stable_test])
     assert excinfo.value.code == 0
 
 
diff --git a/testing/web-platform/tests/tools/wpt/tox.ini b/testing/web-platform/tests/tools/wpt/tox.ini
index 7e6eb8e42a4c..507171355394 100644
--- a/testing/web-platform/tests/tools/wpt/tox.ini
+++ b/testing/web-platform/tests/tools/wpt/tox.ini
@@ -18,4 +18,5 @@ commands =
   pytest {posargs}
 
 passenv =
+  DISPLAY
   TASKCLUSTER_ROOT_URL