WIP: Rewrite as MailExtension (not yet working).

chrome/content/unsafelinks.js → background.js

-// Listen for the "window loaded" event and initialize.
-window.addEventListener("load", function load(event) {
-    window.removeEventListener("load", load, false);
-    unsafelinks.init();
-}, false);
-
 var unsafelinks = {
-    init: function() {
-        // Listen for the "message loaded" event, if this is a message window.
-        var messagepane = document.getElementById("messagepane");
-        if (messagepane) {
-            messagepane.addEventListener("load", unsafelinks.onMessageLoad, true);
+
+    unsafelink: function(messageHeader) {
+        // Request the full message contents so we can do text replacement.
+        browser.messages.getFull(messageHeader.id).then(unsafelinks.replaceInAllMessageParts);
+    },
+
+    replaceInAllMessageParts(messageOrPart) {
+        // Iterate over each "part" of the message (i.e. text, html, etc.)
+        for (partId in messageOrPart.parts) {
+            part = messageOrPart.parts[partId];
+            // Handle this part, if it has a body.
+            if ('body' in part) {
+                unsafelinks.replace(part);
+            }
+            // Recursively handle sub-parts.
+            if ('parts' in part) {
+                unsafelinks.replaceInAllMessageParts(part);
+            }
         }
     },
 
-    onMessageLoad: function(event) {
+    replace: function(messagePart) {
         // Replace each safelinks URL in the message body with the original URL.
-        var body = event.originalTarget.body;
-        body.innerHTML = body.innerHTML.replace(unsafelinks.urlRegex, unsafelinks.replacer);
+        messagePart.body = part.body.replace(unsafelinks.urlRegex, unsafelinks.replacer);
+        // TODO: This doesn't actually update the view!
     },
 
     // Regular expression matching a safelinks-encoded URL.
     urlRegex: /https?:\/\/(?:.+?\.)?safelinks\.protection\.outlook\.com\/([A-Za-z0-9\-\._~:\/\?#\[\]@!$&'\(\)\*\+,;\=%]*)/gi,
 
-    replacer: function(url, queryString){
+    replacer: function(url, queryString) {
         // Extract the "url" parameter from the URL, if it exists.
         var params = new URLSearchParams(queryString);
         if (params.has('url')) {
@@ -31,4 +38,13 @@ var unsafelinks = {
             return url;
         }
     },
+
+    reloadTab: function(tabId) {
+        browser.mailTabs.update(tabId, {});
+    }
 };
+
+browser.messageDisplay.onMessageDisplayed.addListener((tabId, message) => {
+    unsafelinks.unsafelink(message);
+    unsafelinks.reloadTab(tabId);
+});

chrome.manifest

-content     unsafelinks    chrome/content/
-overlay chrome://messenger/content/messenger.xul chrome://unsafelinks/content/unsafelinks.xul
\ No newline at end of file

chrome/content/unsafelinks.xul

-<?xml version="1.0"?>
-<overlay id="unsafelinks" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
-<script type="application/javascript" src="chrome://unsafelinks/content/unsafelinks.js"/>
-</overlay>

install.rdf

-<?xml version="1.0"?>
-<RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
-     xmlns:em="http://www.mozilla.org/2004/em-rdf#">
-  <Description about="urn:mozilla:install-manifest">
-    <em:id>unsafelinks@ant.sr</em:id>
-    <em:name>Un-Safelinks</em:name>
-    <em:description>Replace URLs which have been rewritten by Office 365 Advanced Threat Protection with the original URL.</em:description>
-    <em:version>1.2</em:version>
-	<em:homepageURL>https://ant.sr/unsafelinks</em:homepageURL>
-    <em:targetApplication>
-      <Description>
-        <em:id>{3550f703-e582-4d05-9a08-453d09bdfdc6}</em:id>
-        <em:minVersion>45.8.0</em:minVersion>
-        <em:maxVersion>60.*</em:maxVersion>
-      </Description>
-    </em:targetApplication>
-  </Description>
-</RDF>

manifest.json

+{
+    "manifest_version": 2,
+    "name": "Un-Safelinks",
+    "description": "Replace URLs which have been rewritten by Office 365 Advanced Threat Protection with the original URL.",
+    "version": "1.3",
+    "author": "Anton Sarukhanov",
+    "author": "Anton Sarukhanov",
+    "applications": {
+        "gecko": {
+            "id": "unsafelinks@ant.sr",
+            "strict_min_version": "66.0"
+        }
+    },
+    "permissions": [
+        "messagesRead"
+    ],
+    "background": {
+        "scripts": [
+            "background.js"
+        ]
+    },
+    "icons": {
+        "64": "icon.png"
+    }
+}