Porting it to Firefox Nightly (Firefox version 42 or superior)

firefox-nightly/amp.js

@@ -0,0 +1,63 @@
+var docEl = document.documentElement;
+var isAMP = docEl.hasAttribute('amp') || docEl.hasAttribute('⚡️');
+var observerConfig = { childList: true, subtree: true };
+
+var documentObserver = observeNode(docEl, inspectDocNodes);
+var headObserver;
+
+
+function observeNode(node, cb){
+  var obs = new MutationObserver(function(mutations) {
+    mutations.forEach(function(mutation) {
+      for (var i = 0; i < mutation.addedNodes.length; i++)
+        cb(mutation.addedNodes[i]);
+    });
+  });
+  obs.observe(node, observerConfig);
+  return obs;
+}
+
+function inspectDocNodes(node){
+  if (node.tagName == "LINK" && node.getAttribute('rel').toLowerCase() == 'amphtml'){
+    documentObserver.disconnect();
+    redirect(node);
+  }
+
+  if (node.tagName != "HEAD") return;
+
+  if (isAMP)
+    applyMobileCSS(node);
+  else {
+    queryForMeta(node);
+    headObserver = observeNode(node, inspectHeadNodes);
+    documentObserver.disconnect();
+    // console.log('disconnected from doc')
+  }
+}
+
+function inspectHeadNodes(node) {
+  // node.nodeType == 1 && console.log(node);
+  if (node.tagName == "LINK" && node.getAttribute('rel').toLowerCase() == 'amphtml') {
+      headObserver.disconnect();
+      redirect(node);
+  }
+  // if no match found, headObserver is not disconnected.
+}
+
+function queryForMeta(head) {
+  var node = head.querySelector('link[rel="amphtml"]');
+  if (node)
+    redirect(node);
+}
+
+function redirect(node) {
+  window.location = node.getAttribute("href");
+}
+
+function applyMobileCSS(node) {
+  var css = "body > * { max-width: 600px; margin: 0px auto; }";
+  var style = document.createElement('style');
+  style.type = 'text/css';
+  style.appendChild(document.createTextNode(css));
+  node.appendChild(style);
+}

firefox-nightly/manifest.json

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+{
+  "manifest_version": 2,
+  "name": "⚡️ Desktop AMP",
+  "description": "Load the AMP version of a page if available",
+  "version": "1.2",
+  "author": "Agustin Mendez",
+
+  "applications": {
+    "gecko": {
+      "id": "desktop-amp@matagus",
+      "strict_min_version": "42.0.0"
+    }
+  },
+
+  "content_scripts": [
+    {
+      "matches": ["<all_urls>"],
+      "run_at": "document_start",
+      "js": ["amp.js"]
+    }
+  ],
+
+  "icons": {
+    "16": "icon16.png",
+    "48": "icon48.png",
+    "128": "icon128.png"
+  }
+}