Work-around for Chromium not supporting frameAncestors in webRequest.

src/bg/RequestGuard.js

@@ -261,12 +261,18 @@ var RequestGuard = (() => {
     return redirected;
   }
 
-  function intersectCapabilities(perms, frameAncestors) {
-    if (frameAncestors && frameAncestors.length && ns.sync.cascadeRestrictions) {
-      // cascade top document's restrictions to subframes
-      perms = policy.cascadeRestrictions(perms,
-        frameAncestors[frameAncestors.length - 1].url)
-        .capabilities;
+  function intersectCapabilities(perms, request) {
+    let {frameId, frameAncestors, tabId} = request;
+    if (frameId !== 0 && ns.sync.cascadeRestrictions) {
+      let topUrl = frameAncestors && frameAncestors.length
+        && frameAncestors[frameAncestors.length - 1].url;
+      if (!topUrl) {
+        let tab = TabCache.get(tabId);
+        if (tab) topUrl = tab.url;
+      }
+      if (topUrl) {
+        return ns.policy.cascadeRestrictions(perms, topUrl).capabilities;
+      }
     }
     return perms.capabilities;
   }
@@ -300,7 +306,7 @@ var RequestGuard = (() => {
             !ns.isEnforced(request.tabId) ||
             intersectCapabilities(
                 policy.get(url, documentUrl).perms,
-                request.frameAncestors
+                request
               ).has(policyType);
 
           Content.reportTo(request, allowed, policyType);
@@ -347,7 +353,7 @@ var RequestGuard = (() => {
             }
             capabilities = perms.capabilities;
           } else {
-            capabilities = intersectCapabilities(perms, request.frameAncestors);
+            capabilities = intersectCapabilities(perms, request);
           }
         } // else unrestricted, either globally or per-tab
         if (isMainFrame && !TabStatus.map.has(tabId)) {

src/lib/TabCache.js

@@ -0,0 +1,24 @@
+var TabCache = (() => {
+
+  let cache = new Map();
+
+  browser.tabs.onUpdated.addListener(tab => {
+    cache.set(tab.id, tab);
+  });
+
+  browser.tabs.onRemoved.addListener(tab => {
+    cache.delete(tab.id);
+  });
+  
+  (async () => {
+    for (let tab of await browser.tabs.query({})) {
+      cache.set(tab.id, tab);
+    }
+  })();
+
+  return {
+    get(tabId) {
+      return cache.get(tabId);
+    }
+  };
+})();

src/manifest.json

@@ -47,6 +47,7 @@
       "lib/Messages.js",
       "lib/CSP.js",
       "lib/NetCSP.js",
+      "lib/TabCache.js",
       "common/CapsCSP.js",
       "common/Policy.js",
       "common/locale.js",