diff --git a/3p/integration.js b/3p/integration.js
index 8ca7ab19badf..37560ea25cc6 100644
--- a/3p/integration.js
+++ b/3p/integration.js
@@ -84,11 +84,10 @@ function masterSelection(type) {
 }
 
 /**
- * Draws an optionally synchronously to the DOM.
+ * Draws an embed, optionally synchronously, to the DOM.
  */
 window.draw3p = function() {
-  const fragment = location.hash;
-  const data = fragment ? JSON.parse(fragment.substr(1)) : {};
+  const data = parseFragment(location.hash);
   window.context = data._context;
   window.context.location = parseUrl(data._context.location.href);
   validateParentOrigin(window, window.context.location);
@@ -120,6 +119,9 @@ function triggerDimensions(width, height) {
 }
 
 function nonSensitiveDataPostMessage(type, opt_object) {
+  if (window.parent == window) {
+    return;  // Nothing to do.
+  }
   const object = opt_object || {};
   object.type = type;
   object.sentinel = 'amp-3p';
@@ -173,3 +175,20 @@ export function validateParentOrigin(window, parentLocation) {
       ancestors[0], parentLocation.origin);
   parentLocation.originValidated = true;
 }
+
+/**
+ * Expects the fragment to contain JSON.
+ * @param {string} fragment Value of location.fragment
+ * @return {!JSONObject}
+ * @visibleForTesting
+ */
+export function parseFragment(fragment) {
+  let json = fragment.substr(1);
+  // Some browser, notably Firefox produce an encoded version of the fragment
+  // while most don't. Since we know how the string should start, this is easy
+  // to detect.
+  if (json.indexOf('{%22') == 0) {
+    json = decodeURIComponent(json);
+  }
+  return json ? JSON.parse(json) : {};
+}
diff --git a/test/functional/test-integration.js b/test/functional/test-integration.js
index 24841744d10d..b2c34573d2f8 100644
--- a/test/functional/test-integration.js
+++ b/test/functional/test-integration.js
@@ -17,7 +17,7 @@
 // Tests integration.js
 // Most coverage through test-3p-frame
 
-import {validateParentOrigin} from '../../3p/integration';
+import {validateParentOrigin, parseFragment} from '../../3p/integration';
 import {registrations} from '../../src/3p';
 
 describe('3p integration.js', () => {
@@ -73,4 +73,40 @@ describe('3p integration.js', () => {
         }, parent);
       }).to.throw(/Parent origin mismatch/);
     });
+
+  it('should parse JSON from fragment unencoded (most browsers)', () => {
+    const unencoded = '#{"tweetid":"638793490521001985","width":390,' +
+        '"height":50,"initialWindowWidth":1290,"initialWindowHeight":165,' +
+        '"type":"twitter","_context":{"referrer":"http://localhost:8000/' +
+        'examples.build/","canonicalUrl":"http://localhost:8000/' +
+        'examples.build/amps.html","location":{"href":"http://' +
+        'localhost:8000/examples.build/twitter.amp.max.html"},' +
+        '"mode":{"localDev":true,"development":false,"minified":false}}}';
+    const data = parseFragment(unencoded);
+    expect(data).to.be.object;
+    expect(data.tweetid).to.equal('638793490521001985');
+    expect(data._context.location.href).to.equal(
+        'http://localhost:8000/examples.build/twitter.amp.max.html');
+  });
+
+  it('should parse JSON from fragment encoded (Firefox)', () => {
+    const encoded = '#{%22tweetid%22:%22638793490521001985%22,%22width' +
+        '%22:390,%22height%22:50,%22initialWindowWidth%22:1290,%22initial' +
+        'WindowHeight%22:165,%22type%22:%22twitter%22,%22_context%22:{%22' +
+        'referrer%22:%22http://localhost:8000/examples.build/%22,%22canoni' +
+        'calUrl%22:%22http://localhost:8000/examples.build/amps.html%22,%22' +
+        'location%22:{%22href%22:%22http://localhost:8000/examples.build/t' +
+        'witter.amp.max.html%22},%22mode%22:{%22localDev%22:true,%22develop' +
+        'ment%22:false,%22minified%22:false}}}';
+    const data = parseFragment(encoded);
+    expect(data).to.be.object;
+    expect(data.tweetid).to.equal('638793490521001985');
+    expect(data._context.location.href).to.equal(
+        'http://localhost:8000/examples.build/twitter.amp.max.html');
+  });
+
+  it('should be ok with empty fragment', () => {
+    expect(parseFragment('')).to.be.empty;
+    expect(parseFragment('#')).to.be.empty;
+  });
 });