diff --git a/dom/events/test/file_focus_blur_on_click_in_cross_origin_iframe.html b/dom/events/test/file_focus_blur_on_click_in_cross_origin_iframe.html
new file mode 100644
index 000000000000..51cc05380fb7
--- /dev/null
+++ b/dom/events/test/file_focus_blur_on_click_in_cross_origin_iframe.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<style>
+html, body {
+  height: 100%;
+  margin: 0px;
+  padding: 0px;
+}
+</style>
+<div style="width:100%;height:100%;background-color:blue;"></div>
+<script>
+  document.querySelector("div").addEventListener("click", event => {
+    parent.postMessage("click", "*");
+  });
+  window.onload = () => {
+    parent.postMessage("ready", "*");
+  };
+  document.body.onfocus = () => {
+    parent.postMessage("focus", "*");
+  };
+  document.body.onblur = () => {
+    parent.postMessage("blur", "*");
+  };
+</script>
diff --git a/dom/events/test/file_focus_blur_on_click_in_deep_cross_origin_iframe_inner.html b/dom/events/test/file_focus_blur_on_click_in_deep_cross_origin_iframe_inner.html
new file mode 100644
index 000000000000..57073664020a
--- /dev/null
+++ b/dom/events/test/file_focus_blur_on_click_in_deep_cross_origin_iframe_inner.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<style>
+html, body {
+  height: 100%;
+  margin: 0px;
+  padding: 0px;
+}
+</style>
+<div style="width:100%;height:100%;background-color:blue;"></div>
+<script>
+  document.querySelector("div").addEventListener("click", event => {
+    parent.postMessage("innerclick", "*");
+  });
+  window.onload = () => {
+    parent.postMessage("innerready", "*");
+  };
+  document.body.onfocus = () => {
+    parent.postMessage("innerfocus", "*");
+  };
+  document.body.onblur = () => {
+    parent.postMessage("innerblur", "*");
+  };
+</script>
diff --git a/dom/events/test/file_focus_blur_on_click_in_deep_cross_origin_iframe_middle.html b/dom/events/test/file_focus_blur_on_click_in_deep_cross_origin_iframe_middle.html
new file mode 100644
index 000000000000..1edabb1e802b
--- /dev/null
+++ b/dom/events/test/file_focus_blur_on_click_in_deep_cross_origin_iframe_middle.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<style>
+html, body {
+  height: 200px;
+  margin: 0px;
+  padding: 0px;
+}
+</style>
+<body>
+<script>
+  window.addEventListener("message", event => {
+    parent.postMessage(event.data, "*");
+  });
+  window.onload = () => {
+    parent.postMessage("middleready", "*");
+  };
+  document.body.onfocus = () => {
+    parent.postMessage("middlefocus", "*");
+  };
+  document.body.onblur = () => {
+    parent.postMessage("middleblur", "*");
+  };
+</script>
+<div style="width:100px;height:100px;background-color:gray;"></div>
+<iframe width="100" height="100" src="https://example.org/tests/dom/events/test/file_focus_blur_on_click_in_deep_cross_origin_iframe_inner.html"></iframe>
+<script>
+  document.querySelector("div").addEventListener("click", event => {
+    parent.postMessage("middleclick", "*");
+  });
+</script>
diff --git a/dom/events/test/mochitest.ini b/dom/events/test/mochitest.ini
index b67095531502..60f5bbd29d1e 100644
--- a/dom/events/test/mochitest.ini
+++ b/dom/events/test/mochitest.ini
@@ -236,3 +236,10 @@ skip-if = toolkit == 'android' # Bug 1312791
 [test_unbound_before_in_active_chain.html]
 [test_wheel_zoom_on_form_controls.html]
 skip-if = verify
+[test_focus_blur_on_click_in_cross_origin_iframe.html]
+support-files =
+  file_focus_blur_on_click_in_cross_origin_iframe.html
+[test_focus_blur_on_click_in_deep_cross_origin_iframe.html]
+support-files =
+  file_focus_blur_on_click_in_deep_cross_origin_iframe_inner.html
+  file_focus_blur_on_click_in_deep_cross_origin_iframe_middle.html
diff --git a/dom/events/test/test_focus_blur_on_click_in_cross_origin_iframe.html b/dom/events/test/test_focus_blur_on_click_in_cross_origin_iframe.html
new file mode 100644
index 000000000000..8bf6df747a01
--- /dev/null
+++ b/dom/events/test/test_focus_blur_on_click_in_cross_origin_iframe.html
@@ -0,0 +1,118 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title></title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<script src="/tests/SimpleTest/EventUtils.js"></script>
+<script src="/tests/SimpleTest/paint_listener.js"></script>
+<script src="/tests/gfx/layers/apz/test/mochitest/apz_test_utils.js"></script>
+<script src="/tests/gfx/layers/apz/test/mochitest/apz_test_native_event_utils.js"></script>
+<iframe width=100></iframe>
+<script>
+let state = "start";
+
+const utils = SpecialPowers.DOMWindowUtils;
+
+function synthesizeNativeMouseClick(aElement, aScreenX, aScreenY) {
+  return new Promise(resolve => {
+    utils.sendNativeMouseEvent(aScreenX, aScreenY,
+                               nativeMouseDownEventMsg(), 0, aElement, () => {
+      utils.sendNativeMouseEvent(aScreenX, aScreenY,
+                                 nativeMouseUpEventMsg(),
+                                 0,
+                                 aElement, resolve);
+    });
+  });
+}
+
+function getScreenPosition(aElement, aOffsetX, aOffsetY) {
+  const rect = aElement.getBoundingClientRect();
+  const x = aOffsetX + window.mozInnerScreenX + rect.left;
+  const y = aOffsetY + window.mozInnerScreenY + rect.top;
+  const scale = utils.screenPixelsPerCSSPixel;
+  return [Math.round(x * scale), Math.round(y * scale)];
+}
+
+add_task(async () => {
+  await SimpleTest.promiseFocus();
+
+  const loadsPromise = new Promise((resolve, reject) => {
+    window.addEventListener("message", function listener(event) {
+      if (event.data == "ready") {
+        is(state, "start");
+        state = "ready";
+        resolve();
+      } else {
+        reject("Unexpected message");
+      }
+    }, { once: true });
+  });
+
+  const iframe = document.querySelectorAll("iframe")[0];
+  iframe.src = "https://example.com/tests/dom/events/test/file_focus_blur_on_click_in_cross_origin_iframe.html";
+
+  await loadsPromise;
+
+  // Wait for APZ state stable so that mouse event handling APZ works properly
+  // in out-of-process iframes.
+  await new Promise(resolve => waitForApzFlushedRepaints(resolve));
+
+  // NOTE: synthesizeMouseAtCenter doesn't work for OOP iframes (bug 1528935),
+  // so we use synthesizeNativeMouseClick instead.
+  const [expectedScreenX, expectedScreenY] =
+    getScreenPosition(iframe, 10, 10);
+
+  const firstClickPromise = new Promise((resolve, reject) => {
+    window.addEventListener("message", function listener(event) {
+      if (state == "ready") {
+        if (event.data == "focus") {
+          // Non-Fission case
+          state = "focusbeforeclick";
+        } else if (event.data == "click") {
+          // Fission case: https://bugzilla.mozilla.org/show_bug.cgi?id=1660805
+          state = "clickbeforefocus";
+        } else {
+          ok(false, "Unexpected event");
+        }
+      } else if (state == "focusbeforeclick") {
+        is(event.data, "click", "The second event should be 'click'");
+        state = "firstclick";
+        window.removeEventListener("message", listener);
+        resolve();
+      } else if (state == "clickbeforefocus") {
+        is(event.data, "focus", "The second event should be 'click'");
+        state = "firstclick";
+        window.removeEventListener("message", listener);
+        resolve();
+     } else {
+        reject("Unexpected message");
+      }
+    });
+  });
+
+  await synthesizeNativeMouseClick(iframe, expectedScreenX, expectedScreenY);
+
+  await firstClickPromise;
+
+  SimpleTest.requestFlakyTimeout("Waiting for unwanted events that don't exist on success.");
+
+  const secondClickPromise = new Promise((resolve, reject) => {
+    window.addEventListener("message", function listener(event) {
+      if (state == "firstclick") {
+        is(event.data, "click", "The third event should be 'click' again, not 'blur' or 'focus'.");
+        state = "secondclick";
+        setTimeout(function() {
+          // Wait for potential other unwanted events
+          window.removeEventListener("message", listener);
+          resolve()
+        }, 200);
+      } else {
+        reject("Unexpected message " + event.data);
+      }
+    });
+  });
+
+  await synthesizeNativeMouseClick(iframe, expectedScreenX, expectedScreenY);
+
+  await secondClickPromise;
+});
+</script>
diff --git a/dom/events/test/test_focus_blur_on_click_in_deep_cross_origin_iframe.html b/dom/events/test/test_focus_blur_on_click_in_deep_cross_origin_iframe.html
new file mode 100644
index 000000000000..bb4a3b6d1f0c
--- /dev/null
+++ b/dom/events/test/test_focus_blur_on_click_in_deep_cross_origin_iframe.html
@@ -0,0 +1,148 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title></title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<script src="/tests/SimpleTest/EventUtils.js"></script>
+<script src="/tests/SimpleTest/paint_listener.js"></script>
+<script src="/tests/gfx/layers/apz/test/mochitest/apz_test_utils.js"></script>
+<script src="/tests/gfx/layers/apz/test/mochitest/apz_test_native_event_utils.js"></script>
+<iframe width=100 height=200 scrolling="no"></iframe>
+<script>
+let state = "start";
+
+const utils = SpecialPowers.DOMWindowUtils;
+
+function synthesizeNativeMouseClick(aElement, aScreenX, aScreenY) {
+  return new Promise(resolve => {
+    utils.sendNativeMouseEvent(aScreenX, aScreenY,
+                               nativeMouseDownEventMsg(), 0, aElement, () => {
+      utils.sendNativeMouseEvent(aScreenX, aScreenY,
+                                 nativeMouseUpEventMsg(),
+                                 0,
+                                 aElement, resolve);
+    });
+  });
+}
+
+function getScreenPosition(aElement, aOffsetX, aOffsetY) {
+  const rect = aElement.getBoundingClientRect();
+  const x = aOffsetX + window.mozInnerScreenX + rect.left;
+  const y = aOffsetY + window.mozInnerScreenY + rect.top;
+  const scale = utils.screenPixelsPerCSSPixel;
+  return [Math.round(x * scale), Math.round(y * scale)];
+}
+
+add_task(async () => {
+  await SimpleTest.promiseFocus();
+
+  const loadsPromise = new Promise((resolve, reject) => {
+    let readyMiddle = false;
+    let readyInner = false;
+    window.addEventListener("message", function listener(event) {
+      if (event.data == "middleready") {
+        readyMiddle = true;
+      } else if (event.data == "innerready") {
+        readyInner = true;
+      } else {
+        reject("Unexpected message when waiting for ready " + event.data);
+      }
+      if (readyInner && readyMiddle) {
+        state = "ready";
+        window.removeEventListener("message", listener);
+        resolve();
+      }
+    });
+  });
+
+  const iframe = document.querySelectorAll("iframe")[0];
+  iframe.src = "https://example.com/tests/dom/events/test/file_focus_blur_on_click_in_deep_cross_origin_iframe_middle.html";
+
+  await loadsPromise;
+
+  // Wait for APZ state stable so that mouse event handling APZ works properly
+  // in out-of-process iframes.
+  await new Promise(resolve => waitForApzFlushedRepaints(resolve));
+
+  // NOTE: synthesizeMouseAtCenter doesn't work for OOP iframes (bug 1528935),
+  // so we use synthesizeNativeMouseClick instead.
+  const [expectedScreenX, expectedScreenY] =
+    getScreenPosition(iframe, 10, 10);
+
+  const firstClickPromise = new Promise((resolve, reject) => {
+    window.addEventListener("message", function listener(event) {
+      if (state == "ready") {
+        if (event.data == "innerfocus") {
+          // Non-Fission case
+          state = "innerfocusbeforeclick";
+        } else if (event.data == "innerclick") {
+          // Fission case: https://bugzilla.mozilla.org/show_bug.cgi?id=1660805
+          state = "innerclickbeforefocus";
+        } else if (event.data == "middlefocus") {
+          // https://bugzilla.mozilla.org/show_bug.cgi?id=1661227
+          todo(false, "Ignoring extra middlefocus.");
+        } else {
+          is(event.data, "neverthisevent", "Unexpected event (first click)");
+        }
+      } else if (state == "innerfocusbeforeclick") {
+        is(event.data, "innerclick", "The second event should be 'innerclick'");
+        state = "firstclick";
+        window.removeEventListener("message", listener);
+        resolve();
+      } else if (state == "innerclickbeforefocus") {
+        is(event.data, "innerfocus", "The second event should be 'innerfocus'");
+        state = "firstclick";
+        window.removeEventListener("message", listener);
+        resolve();
+     } else {
+        reject("Unexpected message in firstClickPromise " + event.data);
+      }
+    });
+  });
+
+  await synthesizeNativeMouseClick(iframe, expectedScreenX, expectedScreenY + 110);
+
+  await firstClickPromise;
+
+  SimpleTest.requestFlakyTimeout("Waiting for unwanted events that don't exist on success.");
+
+  const secondClickPromise = new Promise((resolve, reject) => {
+    window.addEventListener("message", function listener(event) {
+      if (state == "firstclick") {
+        is(event.data, "middlefocus", "The third event should be 'middlefocus'.");
+        state = "middlefocusbeforeclick";
+      } else if (state == "middlefocusbeforeclick") {
+        // The order of blur and click is non-deterministic even in the non-Fission case.
+        if (event.data == "middleclick") {
+          state = "waitingforinnerblurafterclick";
+        } else if (event.data == "innerblur") {
+          state = "innerblurbeforeclick";
+        } else {
+          is(event.data, "neverthisevent", "Unexpected event (first click)");
+        }
+      } else if (state == "waitingforinnerblurafterclick") {
+        is(event.data, "innerblur", "The fifth event should be 'innerblur'.");
+        state = "secondclick";
+        setTimeout(function() {
+          // Wait for potential other unwanted events
+          window.removeEventListener("message", listener);
+          resolve()
+        }, 200);
+      } else if (state == "innerblurbeforeclick") {
+        is(event.data, "middleclick", "The fifth event should be 'middleclick'.");
+        state = "secondclick";
+        setTimeout(function() {
+          // Wait for potential other unwanted events
+          window.removeEventListener("message", listener);
+          resolve()
+        }, 200);
+      } else {
+        reject("Unexpected message in secondClickPromise " + event.data);
+      }
+    });
+  });
+
+  await synthesizeNativeMouseClick(iframe, expectedScreenX, expectedScreenY);
+
+  await secondClickPromise;
+});
+</script>
