diff --git a/src/js/messaging.js b/src/js/messaging.js
index c8f5808af..1aa59195b 100644
--- a/src/js/messaging.js
+++ b/src/js/messaging.js
@@ -345,6 +345,7 @@ const onMessage = function(request, sender, callback) {
     case 'setWhitelist':
         µb.netWhitelist = µb.whitelistFromString(request.whitelist);
         µb.saveWhitelist();
+        µb.filteringBehaviorChanged();
         break;
 
     case 'toggleHostnameSwitch':
diff --git a/src/js/scriptlet-filtering.js b/src/js/scriptlet-filtering.js
index 595ed911b..037f399e0 100644
--- a/src/js/scriptlet-filtering.js
+++ b/src/js/scriptlet-filtering.js
@@ -67,7 +67,12 @@ const contentScriptRegisterer = new (class {
     constructor() {
         this.hostnameToDetails = new Map();
         if ( browser.contentScripts === undefined ) { return; }
-        µb.onEvent('filteringBehaviorChanged', ( ) => {
+        µb.onEvent('filteringBehaviorChanged', ev => {
+            const details = ev.detail;
+            if ( details instanceof Object ) {
+                if ( details.direction > 0 ) { return; }
+                if ( details.hostname ) { return this.flush(details.hostname); }
+            }
             this.reset();
         });
     }
@@ -100,6 +105,15 @@ const contentScriptRegisterer = new (class {
         this.hostnameToDetails.delete(hostname);
         this.unregisterHandle(details.handle);
     }
+    flush(hostname) {
+        if ( hostname === '*' ) { return this.reset(); }
+        for ( const hn of this.hostnameToDetails.keys() ) {
+            if ( hn.endsWith(hostname) === false ) { continue; }
+            const pos = hn.length - hostname.length;
+            if ( pos !== 0 && hn.charCodeAt(pos-1) !== 0x2E /* . */ ) { continue; }
+            this.unregister(hn);
+        }
+    }
     reset() {
         if ( this.hostnameToDetails.size === 0 ) { return; }
         for ( const details of this.hostnameToDetails.values() ) {
diff --git a/src/js/storage.js b/src/js/storage.js
index 2b1a81594..a8e0a7c81 100644
--- a/src/js/storage.js
+++ b/src/js/storage.js
@@ -364,7 +364,6 @@ import {
         netWhitelist: this.arrayFromWhitelist(this.netWhitelist)
     });
     this.netWhitelistModifyTime = Date.now();
-    µb.filteringBehaviorChanged();
 };
 
 /******************************************************************************/
diff --git a/src/js/ublock.js b/src/js/ublock.js
index a02ee6f1b..7f902af38 100644
--- a/src/js/ublock.js
+++ b/src/js/ublock.js
@@ -147,6 +147,7 @@ const matchBucket = function(url, hostname, bucket, start) {
         }
         bucket.push(directive);
         this.saveWhitelist();
+        µb.filteringBehaviorChanged({ hostname: targetHostname });
         return true;
     }
 
@@ -187,6 +188,7 @@ const matchBucket = function(url, hostname, bucket, start) {
         }
     }
     this.saveWhitelist();
+    µb.filteringBehaviorChanged({ direction: 1 });
     return true;
 };
 
@@ -465,7 +467,8 @@ const matchBucket = function(url, hostname, bucket, start) {
 // (but not really) redundant rules led to this issue.
 
 µb.toggleFirewallRule = function(details) {
-    let { srcHostname, desHostname, requestType, action } = details;
+    const { desHostname, requestType, action } = details;
+    let { srcHostname } = details;
 
     if ( action !== 0 ) {
         sessionFirewall.setCell(
@@ -495,8 +498,7 @@ const matchBucket = function(url, hostname, bucket, start) {
             permanentFirewall.unsetCell(
                 srcHostname,
                 desHostname,
-                requestType,
-                action
+                requestType
             );
         }
         this.savePermanentFirewallRules();
@@ -521,8 +523,11 @@ const matchBucket = function(url, hostname, bucket, start) {
     // https://github.com/chrisaljoudi/uBlock/issues/420
     cosmeticFilteringEngine.removeFromSelectorCache(srcHostname, 'net');
 
-    // Flush memory cache
-    µb.filteringBehaviorChanged();
+    // Flush caches
+    µb.filteringBehaviorChanged({
+        direction: action === 1 ? 1 : 0,
+        hostname: srcHostname,
+    });
 
     if ( details.tabId === undefined ) { return; }
 
@@ -603,12 +608,15 @@ const matchBucket = function(url, hostname, bucket, start) {
             break;
     }
 
-    // Flush memory cache if needed
+    // Flush caches if needed
     if ( newState ) {
         switch ( details.name ) {
             case 'no-scripting':
             case 'no-remote-fonts':
-                µb.filteringBehaviorChanged();
+                µb.filteringBehaviorChanged({
+                    direction: details.state ? 1 : 0,
+                    hostname: details.hostname,
+                });
                 break;
             default:
                 break;
diff --git a/src/js/utils.js b/src/js/utils.js
index 09e54eb15..9f94aeb25 100644
--- a/src/js/utils.js
+++ b/src/js/utils.js
@@ -134,13 +134,13 @@ import µb from './background.js';
 
 /******************************************************************************/
 
-µb.fireEvent = function(name) {
+µb.fireEvent = function(name, details = undefined) {
     if (
         self instanceof Object &&
         self.dispatchEvent instanceof Function &&
         self.CustomEvent instanceof Function
     ) {
-        self.dispatchEvent(new CustomEvent(name));
+        self.dispatchEvent(new CustomEvent(name, { detail: details }));
     }
 };
 
@@ -155,9 +155,11 @@ import µb from './background.js';
 
 /******************************************************************************/
 
-µb.filteringBehaviorChanged = function() {
-    vAPI.net.handlerBehaviorChanged();
-    this.fireEvent('filteringBehaviorChanged');
+µb.filteringBehaviorChanged = function(details = {}) {
+    if ( typeof details.direction !== 'number' || details.direction >= 0 ) {
+        vAPI.net.handlerBehaviorChanged();
+    }
+    this.fireEvent('filteringBehaviorChanged', details);
 };
 
 /******************************************************************************/