diff --git a/gfx/layers/apz/test/mochitest/helper_hittest_spam.html b/gfx/layers/apz/test/mochitest/helper_hittest_spam.html
index 305d8677bc4b..cace5491a505 100644
--- a/gfx/layers/apz/test/mochitest/helper_hittest_spam.html
+++ b/gfx/layers/apz/test/mochitest/helper_hittest_spam.html
@@ -21,7 +21,7 @@
 <body>
 <script type="application/javascript">
 
-var SPAM_LIMIT = 1000; // bigger numbers make the test run longer
+var SPAM_LIMIT = 200; // bigger numbers make the test run longer
 
 // This function adds and removes a scrollable div very rapidly (via
 // setTimeout(0) self-scheduling). This causes very frequent layer
diff --git a/gfx/layers/apz/test/mochitest/mochitest.ini b/gfx/layers/apz/test/mochitest/mochitest.ini
index eb0260bbbd2c..1ad453624ac9 100644
--- a/gfx/layers/apz/test/mochitest/mochitest.ini
+++ b/gfx/layers/apz/test/mochitest/mochitest.ini
@@ -86,7 +86,7 @@
     toolkit == 'cocoa'  # synthesized wheel smooth-scrolling not supported on OS X
     xorigin  # JavaScript error: http://mochi.test:8888/tests/gfx/layers/apz/test/mochitest/apz_test_native_event_utils.js, line 10: Error: Permission denied to access property "getResolution"
 [test_wheel_scroll.html]
-  skip-if = 
+  skip-if =
     os == 'android'  # wheel events not supported on mobile
     xorigin  # Hangs
 [test_wheel_transactions.html]
@@ -97,7 +97,11 @@
   skip-if =
     toolkit == 'android'  # wheel events not supported on mobile
     xorigin  # Hangs
-[test_group_hittest.html]
+[test_group_hittest-1.html]
+  skip-if =
+    toolkit == 'android'  # mouse events not supported on mobile
+    xorigin  # Hangs
+[test_group_hittest-2.html]
   skip-if =
     toolkit == 'android'  # mouse events not supported on mobile
     xorigin  # Hangs
diff --git a/gfx/layers/apz/test/mochitest/test_group_hittest-1.html b/gfx/layers/apz/test/mochitest/test_group_hittest-1.html
new file mode 100644
index 000000000000..34bf245d6cde
--- /dev/null
+++ b/gfx/layers/apz/test/mochitest/test_group_hittest-1.html
@@ -0,0 +1,59 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Various hit-testing tests that spawn in new windows - Part 1</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript" src="apz_test_utils.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+var prefs = [
+  // Turn off displayport expiry so that we don't miss failures where the
+  // displayport is set and then expires before we get around to doing the
+  // hit-test inside the activated scrollframe.
+  ["apz.displayport_expiry_ms", 0],
+  // Always layerize the scrollbar track, so as to get consistent results
+  // across platforms. Eventually we should probably get rid of this and make
+  // the tests more robust in terms of testing all the different cross-platform
+  // variations.
+  ["layout.scrollbars.always-layerize-track", true],
+  // We need this pref to allow the synthetic mouse events to propagate to APZ,
+  // and to allow the MozMouseHittest event in particular to be dispatched to
+  // APZ as a MouseInput so the hit result is recorded.
+  ["test.events.async.enabled", true],
+  // Turns on APZTestData logging which we use to obtain the hit test results.
+  ["apz.test.logging_enabled", true],
+];
+
+var overscroll_prefs = [...prefs,
+                        ["apz.overscroll.enabled", true],
+                        ["apz.overscroll.test_async_scroll_offset.enabled", true],
+                       ];
+
+var subtests = [
+  {"file": "helper_hittest_basic.html", "prefs": prefs},
+  {"file": "helper_hittest_fixed_in_scrolled_transform.html", "prefs": prefs},
+  {"file": "helper_hittest_float_bug1434846.html", "prefs": prefs},
+  {"file": "helper_hittest_float_bug1443518.html", "prefs": prefs},
+  {"file": "helper_hittest_checkerboard.html", "prefs": prefs},
+  {"file": "helper_hittest_backface_hidden.html", "prefs": prefs},
+  {"file": "helper_hittest_touchaction.html", "prefs": prefs},
+  {"file": "helper_hittest_nested_transforms_bug1459696.html", "prefs": prefs},
+  {"file": "helper_hittest_sticky_bug1478304.html", "prefs": prefs},
+  {"file": "helper_hittest_clipped_fixed_modal.html", "prefs": prefs},
+];
+
+if (isApzEnabled()) {
+  SimpleTest.waitForExplicitFinish();
+  window.onload = function() {
+    runSubtestsSeriallyInFreshWindows(subtests)
+    .then(SimpleTest.finish, SimpleTest.finishWithFailure);
+  };
+}
+
+  </script>
+</head>
+<body>
+</body>
+</html>
diff --git a/gfx/layers/apz/test/mochitest/test_group_hittest.html b/gfx/layers/apz/test/mochitest/test_group_hittest-2.html
similarity index 77%
rename from gfx/layers/apz/test/mochitest/test_group_hittest.html
rename to gfx/layers/apz/test/mochitest/test_group_hittest-2.html
index dc7dbad5214e..146e66d27083 100644
--- a/gfx/layers/apz/test/mochitest/test_group_hittest.html
+++ b/gfx/layers/apz/test/mochitest/test_group_hittest-2.html
@@ -2,7 +2,7 @@
 <html>
 <head>
   <meta charset="utf-8">
-  <title>Various hit-testing tests that spawn in new windows</title>
+  <title>Various hit-testing tests that spawn in new windows - Part 2</title>
   <script src="/tests/SimpleTest/SimpleTest.js"></script>
   <script type="application/javascript" src="apz_test_utils.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
@@ -32,23 +32,14 @@ var overscroll_prefs = [...prefs,
                        ];
 
 var subtests = [
-  {"file": "helper_hittest_basic.html", "prefs": prefs},
-  {"file": "helper_hittest_fixed_in_scrolled_transform.html", "prefs": prefs},
-  {"file": "helper_hittest_float_bug1434846.html", "prefs": prefs},
-  {"file": "helper_hittest_float_bug1443518.html", "prefs": prefs},
-  {"file": "helper_hittest_checkerboard.html", "prefs": prefs},
-  {"file": "helper_hittest_backface_hidden.html", "prefs": prefs},
-  {"file": "helper_hittest_touchaction.html", "prefs": prefs},
-  {"file": "helper_hittest_nested_transforms_bug1459696.html", "prefs": prefs},
-  {"file": "helper_hittest_sticky_bug1478304.html", "prefs": prefs},
-  {"file": "helper_hittest_clipped_fixed_modal.html", "prefs": prefs},
   {"file": "helper_hittest_pointerevents_svg.html", "prefs": prefs},
   {"file": "helper_hittest_clippath.html", "prefs": prefs},
   {"file": "helper_hittest_hoisted_scrollinfo.html", "prefs": prefs},
-  {"file": "helper_hittest_spam.html", "prefs": prefs},
   {"file": "helper_hittest_hidden_inactive_scrollframe.html", "prefs": prefs},
   {"file": "helper_hittest_overscroll.html", "prefs": overscroll_prefs},
   {"file": "helper_hittest_overscroll_subframe.html", "prefs": overscroll_prefs},
+  // This test should be at the end, because it's prone to timeout.
+  {"file": "helper_hittest_spam.html", "prefs": prefs},
 ];
 
 function addConditionalTests(tests) {
@@ -58,9 +49,11 @@ function addConditionalTests(tests) {
   var utils = SpecialPowers.getDOMWindowUtils(window);
   var isWebRender = utils.layerManagerType.startsWith("WebRender");
   if (isWebRender) {
-    tests = tests.concat([
+    // Add new tests at the beginning, to ensure the final test remains in
+    // the final position.
+    tests = [
       {"file": "helper_hittest_deep_scene_stack.html", "prefs": prefs},
-    ]);
+    ].concat(tests);
   }
   return tests;
 }
