Recursive webgl context monkeypatching across same origin windows (concept/patch by skriptimaahinen).

src/content/webglHook.js

@@ -1,28 +1,91 @@
 ns.on("capabilities", event => {
   debug("WebGL Hook", document.URL, document.documentElement && document.documentElement.innerHTML, ns.capabilities); // DEV_ONLY
   if (ns.allows("webgl")) return;
-  let proto = HTMLCanvasElement.prototype;
-  let getContext = proto.getContext;
-  exportFunction(function(type, ...rest) {
-    if (type && type.toLowerCase().includes("webgl")) {
-      let request = {
-        id: "noscript-webgl",
-        type: "webgl",
-        url: document.URL,
-        documentUrl: document.URL,
-        embeddingDocument: true,
-      };
-      seen.record({policyType: "webgl", request, allowed: false});
-      try {
-        let ph = PlaceHolder.create("webgl", request);
-        ph.replace(this);
-        PlaceHolder.listen();
-      } catch (e) {
-        error(e);
-      }
-      notifyPage();
-      return {};
+
+  // win: window object to modify.
+  // modifyTarget: callback to function that modifies the desired properties
+  //                or methods. Callback must take target window as argument.
+  function modifyWindow(win, modifyTarget) {
+    try {
+      modifyTarget(win);
+      modifyWindowOpenMethod(win, modifyTarget);
+      modifyFramingElements(win, modifyTarget);
+    } catch (e) {
+      if (e instanceof DOMException && e.name === "SecurityError") {
+        // In case someone tries to access SOP restricted window.
+        // We can just ignore this.
+      } else throw e;
     }
-    return getContext.call(this, type, ...rest);
-  }, proto, {defineAs: "getContext"});  
+  }
+
+  function modifyWindowOpenMethod(win, modifyTarget) {
+    let windowOpen = win.wrappedJSObject ? win.wrappedJSObject.open : win.open;
+    exportFunction(function(...args) {
+      let newWin = windowOpen.call(this, ...args);
+      if (newWin) modifyWindow(newWin, modifyTarget);
+      return newWin;
+    }, win, {defineAs: "open"});
+  }
+
+  function modifyFramingElements(win, modifyTarget) {
+    for (let property of ["contentWindow", "contentDocument"]) {
+      for (let interface of ["Frame", "IFrame", "Object"]) {
+        let proto = win[`HTML${interface}Element`].prototype;
+        modifyContentProperties(proto, property, modifyTarget)
+      }
+    }
+  }
+
+  function modifyContentProperties(proto, property, modifyTarget) {
+    let descriptor = Object.getOwnPropertyDescriptor(proto, property);
+    let origGetter = descriptor.get;
+    let replacementFn;
+
+    if (property === "contentWindow") { replacementFn = function() {
+      let win = origGetter.call(this);
+      if (win) modifyWindow(win, modifyTarget);
+      return win;
+    }}
+    if (property === "contentDocument") { replacementFn = function() {
+      let document = origGetter.call(this);
+      if (document && document.defaultView) modifyWindow(document.defaultView, modifyTarget);
+      return document;
+    }}
+
+    descriptor.get = exportFunction(replacementFn, proto, {defineAs: `get $property`});
+    let wrappedProto = proto.wrappedJSObject || proto;
+    Object.defineProperty(wrappedProto, property, descriptor);
+  }
+
+  //
+
+  function modifyGetContext(win) {
+      let proto = win.HTMLCanvasElement.prototype;
+      let getContext = proto.getContext;
+      exportFunction(function(type, ...rest) {
+        if (type && type.toLowerCase().includes("webgl")) {
+          let request = {
+            id: "noscript-webgl",
+            type: "webgl",
+            url: document.URL,
+            documentUrl: document.URL,
+            embeddingDocument: true,
+          };
+          seen.record({policyType: "webgl", request, allowed: false});
+          try {
+            let ph = PlaceHolder.create("webgl", request);
+            ph.replace(this);
+            PlaceHolder.listen();
+          } catch (e) {
+            error(e);
+          }
+          notifyPage();
+          return {};
+        }
+        return getContext.call(this, type, ...rest);
+      }, proto, {defineAs: "getContext"});
+  }
+
+  modifyWindow(window, modifyGetContext);
+
 });