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diff --git a/devtools/shared/heapsnapshot/tests/xpcshell/test_DominatorTree_06.js b/devtools/shared/heapsnapshot/tests/xpcshell/test_DominatorTree_06.js
new file mode 100644
index 0000000000..fdd4191c5f
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+++ b/devtools/shared/heapsnapshot/tests/xpcshell/test_DominatorTree_06.js
@@ -0,0 +1,62 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+"use strict";
+
+// Test that the retained size of a node is the sum of its children retained
+// sizes plus its shallow size.
+
+// Note that we don't assert directly, only if we get an unexpected
+// value. There are just way too many nodes in the heap graph to assert for
+// every one. This test would constantly time out and assertion messages would
+// overflow the log size.
+function fastAssert(cond, msg) {
+  if (!cond) {
+    ok(false, msg);
+  }
+}
+
+const COUNT = { by: "count", count: false, bytes: true };
+
+function run_test() {
+  const path = saveNewHeapSnapshot();
+  const snapshot = ChromeUtils.readHeapSnapshot(path);
+  const dominatorTree = snapshot.computeDominatorTree();
+
+  // Do a traversal of the dominator tree and assert the relationship between
+  // retained size, shallow size, and children's retained sizes.
+
+  const root = dominatorTree.root;
+  const stack = [root];
+  while (stack.length) {
+    const top = stack.pop();
+
+    const children = dominatorTree.getImmediatelyDominated(top);
+
+    const topRetainedSize = dominatorTree.getRetainedSize(top);
+    const topShallowSize = snapshot.describeNode(COUNT, top).bytes;
+    fastAssert(
+      topShallowSize <= topRetainedSize,
+      "The shallow size should be less than or equal to the " + "retained size"
+    );
+
+    let sumOfChildrensRetainedSizes = 0;
+    for (let i = 0; i < children.length; i++) {
+      sumOfChildrensRetainedSizes += dominatorTree.getRetainedSize(children[i]);
+      stack.push(children[i]);
+    }
+
+    fastAssert(
+      sumOfChildrensRetainedSizes <= topRetainedSize,
+      "The sum of the children's retained sizes should be less than " +
+        "or equal to the retained size"
+    );
+    fastAssert(
+      sumOfChildrensRetainedSizes + topShallowSize === topRetainedSize,
+      "The sum of the children's retained sizes plus the shallow " +
+        "size should be equal to the retained size"
+    );
+  }
+
+  ok(true, "Successfully walked the tree");
+  do_test_finished();
+}