diff --git a/src/js/contentscript.js b/src/js/contentscript.js
index 6f29027e1..3656b4177 100644
--- a/src/js/contentscript.js
+++ b/src/js/contentscript.js
@@ -1735,7 +1735,6 @@ vAPI.injectScriptlet = function(doc, text) {
         vAPI.messaging.send('contentscript', {
             what: 'retrieveContentScriptParameters',
             url: vAPI.effectiveSelf.location.href,
-            charset: document.characterSet,
         }).then(response => {
             bootstrapPhase1(response);
         });
diff --git a/src/js/messaging.js b/src/js/messaging.js
index a76ca5d82..a8cb08450 100644
--- a/src/js/messaging.js
+++ b/src/js/messaging.js
@@ -557,6 +557,13 @@ const retrieveContentScriptParameters = function(sender, request) {
         return;
     }
 
+    // A content script may not always be able to successfully look up the
+    // effective context, hence in such case we try again to look up here
+    // using cached information about embedded frames.
+    if ( frameId !== 0 && request.url.startsWith('about:') ) {
+        request.url = pageStore.getEffectiveFrameURL(sender);
+    }
+
     const noCosmeticFiltering = pageStore.noCosmeticFiltering === true;
 
     const response = {
diff --git a/src/js/pagestore.js b/src/js/pagestore.js
index 0444e2018..5667878fb 100644
--- a/src/js/pagestore.js
+++ b/src/js/pagestore.js
@@ -181,12 +181,13 @@ const frameStoreJunkyard = [];
 const frameStoreJunkyardMax = 50;
 
 const FrameStore = class {
-    constructor(frameURL) {
-        this.init(frameURL);
+    constructor(frameURL, parentId) {
+        this.init(frameURL, parentId);
     }
 
-    init(frameURL) {
+    init(frameURL, parentId) {
         this.t0 = Date.now();
+        this.parentId = parentId;
         this.exceptCname = undefined;
         this.clickToLoad = false;
         this.rawURL = frameURL;
@@ -199,7 +200,6 @@ const FrameStore = class {
     }
 
     dispose() {
-        this.exceptCname = undefined;
         this.rawURL = this.hostname = this.domain = '';
         if ( frameStoreJunkyard.length < frameStoreJunkyardMax ) {
             frameStoreJunkyard.push(this);
@@ -207,12 +207,12 @@ const FrameStore = class {
         return null;
     }
 
-    static factory(frameURL) {
+    static factory(frameURL, parentId = -1) {
         const entry = frameStoreJunkyard.pop();
         if ( entry === undefined ) {
-            return new FrameStore(frameURL);
+            return new FrameStore(frameURL, parentId);
         }
-        return entry.init(frameURL);
+        return entry.init(frameURL, parentId);
     }
 };
 
@@ -277,7 +277,7 @@ const PageStore = class {
 
         this.frameAddCount = 0;
         this.frames = new Map();
-        this.setFrameURL(0, tabContext.rawURL);
+        this.setFrameURL({ url: tabContext.rawURL });
 
         // https://github.com/uBlockOrigin/uBlock-issues/issues/314
         const masterSwitch = tabContext.getNetFilteringSwitch();
@@ -324,7 +324,7 @@ const PageStore = class {
             // As part of https://github.com/chrisaljoudi/uBlock/issues/405
             // URL changed, force a re-evaluation of filtering switch
             this.rawURL = tabContext.rawURL;
-            this.setFrameURL(0, this.rawURL);
+            this.setFrameURL({ url: this.rawURL });
             return this;
         }
 
@@ -375,14 +375,20 @@ const PageStore = class {
         return this.frames.get(frameId) || null;
     }
 
-    setFrameURL(frameId, frameURL) {
+    setFrameURL(details) {
+        let { frameId, url, parentFrameId } = details;
+        if ( frameId === undefined ) { frameId = 0; }
+        if ( parentFrameId === undefined ) { parentFrameId = -1; }
         let frameStore = this.frames.get(frameId);
         if ( frameStore !== undefined ) {
-            return frameURL === frameStore.rawURL
-                ? frameStore
-                : frameStore.init(frameURL);
+            if ( url === frameStore.rawURL ) {
+                frameStore.parentId = parentFrameId;
+            } else {
+                frameStore.init(url, parentFrameId);
+            }
+            return frameStore;
         }
-        frameStore = FrameStore.factory(frameURL);
+        frameStore = FrameStore.factory(url, parentFrameId);
         this.frames.set(frameId, frameStore);
         this.frameAddCount += 1;
         if ( (this.frameAddCount & 0b111111) === 0 ) {
@@ -391,6 +397,20 @@ const PageStore = class {
         return frameStore;
     }
 
+    getEffectiveFrameURL(sender) {
+        let { frameId } = sender;
+        for (;;) {
+            const frameStore = this.getFrameStore(frameId);
+            if ( frameStore === null ) { break; }
+            if ( frameStore.rawURL.startsWith('about:') === false ) {
+                return frameStore.rawURL;
+            }
+            frameId = frameStore.parentId;
+            if ( frameId === -1 ) { break; }
+        }
+        return sender.frameURL;
+    }
+
     // There is no event to tell us a specific subframe has been removed from
     // the main document. The code below will remove subframes which are no
     // longer present in the root document. Removing obsolete subframes is
@@ -851,7 +871,7 @@ const PageStore = class {
     clickToLoad(frameId, frameURL) {
         let frameStore = this.getFrameStore(frameId);
         if ( frameStore === null ) {
-            frameStore = this.setFrameURL(frameId, frameURL);
+            frameStore = this.setFrameURL({ frameId, url: frameURL });
         }
         this.netFilteringCache.forgetResult(
             this.tabHostname,
diff --git a/src/js/tab.js b/src/js/tab.js
index ebdce0c42..fe04dbe08 100644
--- a/src/js/tab.js
+++ b/src/js/tab.js
@@ -875,18 +875,23 @@ vAPI.Tabs = class extends vAPI.Tabs {
     onNavigation(details) {
         super.onNavigation(details);
         const µb = µBlock;
-        if ( details.frameId === 0 ) {
-            µb.tabContextManager.commit(details.tabId, details.url);
-            let pageStore = µb.bindTabToPageStore(details.tabId, 'tabCommitted');
-            if ( pageStore ) {
-                pageStore.journalAddRootFrame('committed', details.url);
+        const { frameId, tabId, url } = details;
+        if ( frameId === 0 ) {
+            µb.tabContextManager.commit(tabId, url);
+            const pageStore = µb.bindTabToPageStore(tabId, 'tabCommitted');
+            if ( pageStore !== null ) {
+                pageStore.journalAddRootFrame('committed', url);
             }
         }
-        if ( µb.canInjectScriptletsNow && µb.URI.isNetworkURI(details.url) ) {
-            const pageStore = µb.pageStoreFromTabId(details.tabId);
-            if ( pageStore !== null && pageStore.getNetFilteringSwitch() ) {
-                µb.scriptletFilteringEngine.injectNow(details);
-            }
+        const pageStore = µb.pageStoreFromTabId(tabId);
+        if ( pageStore === null ) { return; }
+        pageStore.setFrameURL(details);
+        if (
+            µb.canInjectScriptletsNow &&
+            µb.URI.isNetworkURI(url) &&
+            pageStore.getNetFilteringSwitch()
+        ) {
+            µb.scriptletFilteringEngine.injectNow(details);
         }
     }
 
diff --git a/src/js/traffic.js b/src/js/traffic.js
index ce25ef13c..5ebf7586b 100644
--- a/src/js/traffic.js
+++ b/src/js/traffic.js
@@ -113,7 +113,7 @@ const onBeforeRequest = function(details) {
         details.parentFrameId !== -1 &&
         details.aliasURL === undefined
     ) {
-        pageStore.setFrameURL(details.frameId, details.url);
+        pageStore.setFrameURL(details);
     }
 
     if ( result === 2 ) {