1 files changed, 52 insertions, 0 deletions
diff --git a/layout/style/test/test_style_attr_listener.html b/layout/style/test/test_style_attr_listener.html
new file mode 100644
index 0000000000..b824fe7ff4
--- /dev/null
+++ b/layout/style/test/test_style_attr_listener.html
@@ -0,0 +1,52 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Test for Bug 338679 (from bug 1340341)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<div style=""></div>
+<script>
+SimpleTest.waitForExplicitFinish();
+
+// Run the test first with mutation events enabled and then disabled.
+SpecialPowers.pushPrefEnv(
+  { 'set': [['dom.mutation-events.cssom.disabled', false]] },
+  runTest
+);
+
+function runTest(stop) {
+  let div = document.querySelector('div');
+  let expectation;
+  let count = 0;
+  div.style.color = "red";
+  div.addEventListener('DOMAttrModified', function(evt) {
+    count++;
+    is(evt.prevValue, expectation.prevValue, `Previous value for event ${count}`);
+    is(evt.newValue, expectation.newValue, `New value for event ${count}`);
+  });
+  expectation = { prevValue: 'color: red;', newValue: 'color: green;' };
+  div.style.color = "green";
+  expectation = { prevValue: 'color: green;', newValue: '' };
+  div.style.color = '';
+  if (SpecialPowers.getBoolPref("dom.mutation-events.cssom.disabled")) {
+    is(count, 0, "No DOMAttrModified event should be triggered");
+  } else {
+    is(count, 2, "DOMAttrModified events should have been triggered");
+  }
+
+  if (!stop) {
+    div.setAttribute("style", "");
+    SpecialPowers.pushPrefEnv(
+      { 'set': [['dom.mutation-events.cssom.disabled', true]] },
+      function() {
+        runTest(true);
+        SimpleTest.finish();
+      }
+    );
+  }
+}
+</script>
+</body>
+</html>