diff --git a/testing/mozharness/scripts/web_platform_tests.py b/testing/mozharness/scripts/web_platform_tests.py
index 5fc325314c2e..8ce489063070 100755
--- a/testing/mozharness/scripts/web_platform_tests.py
+++ b/testing/mozharness/scripts/web_platform_tests.py
@@ -233,6 +233,12 @@ class WebPlatformTest(TestingMixin, MercurialScript, CodeCoverageMixin, AndroidM
         if not sys.platform.startswith("linux"):
             cmd += ["--exclude=css"]
 
+        if mozinfo.info["os"] == "win" and mozinfo.info["os_version"] == "6.1":
+            # On Windows 7 --install-fonts fails, so fall back to a Firefox-specific codepath
+            self._install_fonts()
+        else:
+            cmd += ["--install-fonts"]
+
         for test_type in test_types:
             cmd.append("--test-type=%s" % test_type)
 
@@ -329,8 +335,6 @@ class WebPlatformTest(TestingMixin, MercurialScript, CodeCoverageMixin, AndroidM
     def run_tests(self):
         dirs = self.query_abs_dirs()
 
-        self._install_fonts()
-
         parser = StructuredOutputParser(config=self.config,
                                         log_obj=self.log_obj,
                                         log_compact=True,
diff --git a/testing/web-platform/mach_commands.py b/testing/web-platform/mach_commands.py
index 9e7601e3c53c..6d3e2a8fec61 100644
--- a/testing/web-platform/mach_commands.py
+++ b/testing/web-platform/mach_commands.py
@@ -78,6 +78,7 @@ class WebPlatformTestsRunnerSetup(MozbuildObject):
         return kwargs
 
     def kwargs_firefox(self, kwargs):
+        import mozinfo
         from wptrunner import wptcommandline
         kwargs = self.kwargs_common(kwargs)
 
@@ -90,7 +91,12 @@ class WebPlatformTestsRunnerSetup(MozbuildObject):
         if kwargs["webdriver_binary"] is None:
             kwargs["webdriver_binary"] = self.get_binary_path("geckodriver", validate_exists=False)
 
-        self.setup_fonts_firefox()
+
+        if mozinfo.info["os"] == "win" and mozinfo.info["os_version"] == "6.1":
+            # On Windows 7 --install-fonts fails, so fall back to a Firefox-specific codepath
+            self.setup_fonts_firefox()
+        else:
+            kwargs["install_fonts"] = True
 
         kwargs = wptcommandline.check_args(kwargs)
 
@@ -141,6 +147,7 @@ class WebPlatformTestsRunnerSetup(MozbuildObject):
                 dest.write(src.read())
 
 
+
 class WebPlatformTestsUpdater(MozbuildObject):
     """Update web platform tests."""
     def setup_logging(self, **kwargs):
diff --git a/testing/web-platform/tests/tools/wptrunner/wptrunner/wptrunner.py b/testing/web-platform/tests/tools/wptrunner/wptrunner/wptrunner.py
index 7ac7b709436c..0a5b1352e212 100644
--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/wptrunner.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/wptrunner.py
@@ -150,7 +150,7 @@ def run_tests(config, test_paths, product, **kwargs):
         if kwargs["install_fonts"]:
             env_extras.append(FontInstaller(
                 font_dir=kwargs["font_dir"],
-                ahem=os.path.join(kwargs["tests_root"], "fonts/Ahem.ttf")
+                ahem=os.path.join(test_paths["/"]["tests_path"], "fonts/Ahem.ttf")
             ))
 
         run_info, test_loader = get_loader(test_paths,