diff --git a/platform/chromium/vapi-background.js b/platform/chromium/vapi-background.js
index 461a8e797..5cc26b5cd 100644
--- a/platform/chromium/vapi-background.js
+++ b/platform/chromium/vapi-background.js
@@ -943,6 +943,7 @@ vAPI.messaging = {
     onFrameworkMessage: function(request, port, callback) {
         const sender = port && port.sender;
         if ( !sender ) { return; }
+        const fromDetails = this.ports.get(port.name) || {};
         const tabId = sender.tab && sender.tab.id || undefined;
         const msg = request.msg;
         switch ( msg.what ) {
@@ -981,12 +982,21 @@ vAPI.messaging = {
             break;
         }
         case 'extendClient':
+            if ( fromDetails.privileged !== true ) { break; }
             vAPI.tabs.executeScript(tabId, {
                 file: '/js/vapi-client-extra.js',
             }).then(( ) => {
                 callback();
             });
             break;
+        case 'localStorage': {
+            if ( fromDetails.privileged !== true ) { break; }
+            const args = msg.args || [];
+            vAPI.localStorage[msg.fn](...args).then(result => {
+                callback(result);
+            });
+            break;
+        }
         case 'userCSS':
             if ( tabId === undefined ) { break; }
             const details = {
@@ -1401,6 +1411,78 @@ vAPI.adminStorage = (( ) => {
 /******************************************************************************/
 /******************************************************************************/
 
+// A localStorage-like object which should be accessible from the
+// background page or auxiliary pages.
+//
+// https://github.com/uBlockOrigin/uBlock-issues/issues/899
+//   Convert into asynchronous access API.
+//
+// Note: vAPI.localStorage should already be defined with the client-side
+//       implementation at this point, but we override with the
+//       background-side implementation.
+vAPI.localStorage = {
+    start: async function() {
+        if ( this.cache instanceof Promise ) { return this.cache; }
+        if ( this.cache instanceof Object ) { return this.cache; }
+        this.cache = webext.storage.local.get('localStorage').then(bin => {
+            this.cache = undefined;
+            try {
+                if (
+                    bin instanceof Object === false ||
+                    bin.localStorage instanceof Object === false
+                ) {
+                    this.cache = {};
+                    const ls = self.localStorage;
+                    for ( let i = 0; i < ls.length; i++ ) {
+                        const key = ls.key(i);
+                        this.cache[key] = ls.getItem(key);
+                    }
+                    webext.storage.local.set({ localStorage: this.cache });
+                } else {
+                    this.cache = bin.localStorage;
+                }
+            } catch(ex) {
+            }
+            if ( this.cache instanceof Object === false ) {
+                this.cache = {};
+            }
+        });
+        return this.cache;
+    },
+    clear: function() {
+        this.cache = {};
+        return webext.storage.local.set({ localStorage: this.cache });
+    },
+    getItem: function(key) {
+        if ( this.cache instanceof Object === false ) {
+            console.info(`localStorage.getItem('${key}') not ready`);
+            return null;
+        }
+        const value = this.cache[key];
+        return value !== undefined ? value : null;
+    },
+    getItemAsync: async function(key) {
+        await this.start();
+        const value = this.cache[key];
+        return value !== undefined ? value : null;
+    },
+    removeItem: async function(key) {
+        this.setItem(key);
+    },
+    setItem: async function(key, value = undefined) {
+        await this.start();
+        if ( value === this.cache[key] ) { return; }
+        this.cache[key] = value;
+        return webext.storage.local.set({ localStorage: this.cache });
+    },
+    cache: undefined,
+};
+
+vAPI.localStorage.start();
+
+/******************************************************************************/
+/******************************************************************************/
+
 // https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage/sync
 
 vAPI.cloud = (( ) => {
diff --git a/platform/chromium/vapi-common.js b/platform/chromium/vapi-common.js
index 34b1d6d64..7fc1c96ad 100644
--- a/platform/chromium/vapi-common.js
+++ b/platform/chromium/vapi-common.js
@@ -216,98 +216,41 @@ vAPI.closePopup = function() {
 
 // A localStorage-like object which should be accessible from the
 // background page or auxiliary pages.
-// This storage is optional, but it is nice to have, for a more polished user
-// experience.
-//
-// https://github.com/gorhill/uBlock/issues/2824
-//   Use a dummy localStorage if for some reasons it's not available.
-//
-// https://github.com/gorhill/uMatrix/issues/840
-//   Always use a wrapper to seamlessly handle exceptions
 //
 // https://github.com/uBlockOrigin/uBlock-issues/issues/899
 //   Convert into asynchronous access API.
 
 vAPI.localStorage = {
-    start: function() {
-        if ( this.cache instanceof Promise ) { return this.cache; }
-        if ( this.cache instanceof Object ) { return Promise.resolve(); }
-        const onChanged = (changes, area) => {
-            if (
-                area !== 'local' ||
-                changes instanceof Object === false ||
-                changes.localStorage instanceof Object === false
-            ) {
-                return;
-            }
-            const newValue = changes.localStorage.newValue;
-            this.cache = newValue instanceof Object ? newValue : {};
-        };
-        this.cache = new Promise(resolve => {
-            browser.storage.local.get('localStorage', bin => {
-                this.cache = undefined;
-                try {
-                    if (
-                        bin instanceof Object === false ||
-                        bin.localStorage instanceof Object === false
-                    ) {
-                        this.cache = {};
-                        const ls = self.localStorage;
-                        for ( let i = 0; i < ls.length; i++ ) {
-                            const key = ls.key(i);
-                            this.cache[key] = ls.getItem(key);
-                        }
-                        browser.storage.local.set({ localStorage: this.cache });
-                    } else {
-                        this.cache = bin.localStorage;
-                    }
-                } catch(ex) {
-                }
-                if ( this.cache instanceof Object === false ) {
-                    this.cache = {};
-                }
-                resolve();
-                browser.storage.onChanged.addListener(onChanged);
-                self.addEventListener('beforeunload', ( ) => {
-                    this.cache = undefined;
-                    browser.storage.onChanged.removeListener(onChanged);
-                });
-            });
-        });
-        return this.cache;
-    },
     clear: function() {
-        this.cache = {};
-        return browser.storage.local.set({ localStorage: this.cache });
-    },
-    getItem: function(key) {
-        if ( this.cache instanceof Object === false ) {
-            console.info(`localStorage.getItem('${key}') not ready`);
-            return null;
-        }
-        const value = this.cache[key];
-        return value !== undefined ? value : null;
+        vAPI.messaging.send('vapi', {
+            what: 'localStorage',
+            fn: 'clear',
+        });
     },
     getItemAsync: function(key) {
-        return this.start().then(( ) => {
-            const value = this.cache[key];
-            return value !== undefined ? value : null;
+        return vAPI.messaging.send('vapi', {
+            what: 'localStorage',
+            fn: 'getItemAsync',
+            args: [ key ],
         });
     },
     removeItem: function(key) {
-        this.setItem(key);
-    },
-    setItem: function(key, value = undefined) {
-        return this.start().then(( ) => {
-            if ( value === this.cache[key] ) { return; }
-            this.cache[key] = value;
-            return browser.storage.local.set({ localStorage: this.cache });
+        return vAPI.messaging.send('vapi', {
+            what: 'localStorage',
+            fn: 'removeItem',
+            args: [ key ],
+        });
+    },
+    setItem: function(key, value = undefined) {
+        return vAPI.messaging.send('vapi', {
+            what: 'localStorage',
+            fn: 'setItem',
+            args: [ key, value ]
         });
     },
-    cache: undefined,
 };
 
-vAPI.localStorage.start();
+
 
 
 
diff --git a/src/js/1p-filters.js b/src/js/1p-filters.js
index 1cc6cc3c6..28217dd5a 100644
--- a/src/js/1p-filters.js
+++ b/src/js/1p-filters.js
@@ -202,21 +202,29 @@ uDom('#userFiltersRevert').on('click', revertChanges);
 // https://github.com/gorhill/uBlock/issues/3706
 //   Save/restore cursor position
 //
-// CoreMirror reference: https://codemirror.net/doc/manual.html#api_selection
-renderUserFilters().then(( ) => {
-    cmEditor.clearHistory();
-    return vAPI.localStorage.getItemAsync('myFiltersCursorPosition');
-}).then(line => {
-    if ( typeof line === 'number' ) {
-        cmEditor.setCursor(line, 0);
-    }
-    cmEditor.on('cursorActivity', ( ) => {
-        const line = cmEditor.getCursor().line;
-        if ( vAPI.localStorage.getItem('myFiltersCursorPosition') !== line ) {
-            vAPI.localStorage.setItem('myFiltersCursorPosition', line);
+// CodeMirror reference: https://codemirror.net/doc/manual.html#api_selection
+{
+    let curline = 0;
+    let timer;
+
+    renderUserFilters().then(( ) => {
+        cmEditor.clearHistory();
+        return vAPI.localStorage.getItemAsync('myFiltersCursorPosition');
+    }).then(line => {
+        if ( typeof line === 'number' ) {
+            cmEditor.setCursor(line, 0);
         }
+        cmEditor.on('cursorActivity', ( ) => {
+            if ( timer !== undefined ) { return; }
+            if ( cmEditor.getCursor().line === curline ) { return; }
+            timer = vAPI.setTimeout(( ) => {
+                timer = undefined;
+                curline = cmEditor.getCursor().line;
+                vAPI.localStorage.setItem('myFiltersCursorPosition', curline);
+            }, 701);
+        });
     });
-});
+}
 
 cmEditor.on('changes', userFiltersChanged);
 CodeMirror.commands.save = applyChanges;