diff --git a/src/js/contentscript.js b/src/js/contentscript.js
index 4c3b1e681..50f2aa784 100644
--- a/src/js/contentscript.js
+++ b/src/js/contentscript.js
@@ -240,7 +240,7 @@ vAPI.domWatcher = (function() {
             }
         }
         if ( addedNodeLists.length !== 0 || removedNodes ) {
-            safeObserverHandlerTimer.start();
+            safeObserverHandlerTimer.start(1);
         }
         //console.timeEnd('dom watcher/observer handler');
     };
@@ -276,11 +276,9 @@ vAPI.domWatcher = (function() {
         if ( listeners.indexOf(listener) !== -1 ) { return; }
         listeners.push(listener);
         listenerIteratorDirty = true;
-        if ( domIsReady ) {
-            listener.onDOMCreated();
-        } else {
-            startMutationObserver();
-        }
+        if ( domIsReady !== true ) { return; }
+        listener.onDOMCreated();
+        startMutationObserver();
     };
 
     var removeListener = function(listener) {
@@ -1004,6 +1002,7 @@ vAPI.domCollapser = (function() {
 vAPI.domSurveyor = (function() {
     var messaging = vAPI.messaging,
         domFilterer,
+        hostname = '',
         queriedIds = new Set(),
         queriedClasses = new Set(),
         pendingIdNodes = { nodes: [], added: [] },
@@ -1176,7 +1175,7 @@ vAPI.domSurveyor = (function() {
                 'contentscript',
                 {
                     what: 'retrieveGenericCosmeticSelectors',
-                    frameURL: window.location.href,
+                    hostname: hostname,
                     ids: ids.join('\n'),
                     classes: classes.join('\n'),
                     exceptions: domFilterer.exceptions,
@@ -1245,11 +1244,15 @@ vAPI.domSurveyor = (function() {
         }
     };
 
-    if ( vAPI.domWatcher instanceof Object ) {
+    var start = function(details) {
+        if ( vAPI.domWatcher instanceof Object === false ) { return; }
+        hostname = details.hostname;
         vAPI.domWatcher.addListener(domWatcherInterface);
-    }
+    };
 
-    return {};
+    return {
+        start: start
+    };
 })();
 
 /******************************************************************************/
@@ -1270,11 +1273,21 @@ vAPI.domSurveyor = (function() {
             document.removeEventListener('DOMContentLoaded', bootstrapPhase2);
         }
 
-        if ( vAPI instanceof Object && vAPI.domWatcher instanceof Object ) {
+        if ( vAPI instanceof Object === false ) {
+            return;
+        }
+
+        if ( vAPI.domWatcher instanceof Object ) {
             vAPI.domWatcher.start();
         }
 
-        if ( window !== window.top || !vAPI.domFilterer ) { return; }
+        // Element picker works only in top window for now.
+        if (
+            window !== window.top ||
+            vAPI.domFilterer instanceof Object === false
+        ) {
+            return;
+        }
 
         // To send mouse coordinates to main process, as the chrome API fails
         // to provide the mouse position to context menu listeners.
@@ -1375,6 +1388,10 @@ vAPI.domSurveyor = (function() {
             vAPI.injectedScripts = text;
         }
 
+        if ( vAPI.domSurveyor instanceof Object ) {
+            vAPI.domSurveyor.start(cfeDetails);
+        }
+
         // https://github.com/chrisaljoudi/uBlock/issues/587
         // If no filters were found, maybe the script was injected before
         // uBlock's process was fully initialized. When this happens, pages
diff --git a/src/js/cosmetic-filtering.js b/src/js/cosmetic-filtering.js
index 32dfb809e..0696a3d19 100644
--- a/src/js/cosmetic-filtering.js
+++ b/src/js/cosmetic-filtering.js
@@ -1949,7 +1949,10 @@ FilterContainer.prototype.retrieveGenericSelectors = function(request) {
         complexSelectors = this.setRegister1;
     var entry, selectors,
         strEnd, sliceBeg, sliceEnd,
-        selector, bucket, item;
+        selector, bucket;
+
+    var cacheEntry = this.selectorCache.get(request.hostname),
+        previousHits = cacheEntry && cacheEntry.cosmetic || this.setRegister2;
 
     for ( var type in this.lowlyGeneric ) {
         entry = this.lowlyGeneric[type];
@@ -1965,14 +1968,19 @@ FilterContainer.prototype.retrieveGenericSelectors = function(request) {
             if ( entry.simple.has(selector) === false ) { continue; }
             if ( (bucket = entry.complex.get(selector)) !== undefined ) {
                 if ( Array.isArray(bucket) ) {
-                    for ( item of bucket ) {
-                        complexSelectors.add(item);
+                    for ( selector of bucket ) {
+                        if ( previousHits.has(selector) === false ) {
+                            complexSelectors.add(selector);
+                        }
                     }
-                } else {
+                } else if ( previousHits.has(bucket) === false ) {
                     complexSelectors.add(bucket);
                 }
             } else {
-                simpleSelectors.add(entry.prefix + selector);
+                selector = entry.prefix + selector;
+                if ( previousHits.has(selector) === false ) {
+                    simpleSelectors.add(selector);
+                }
             }
         } while ( sliceBeg < strEnd );
     }
@@ -1994,17 +2002,15 @@ FilterContainer.prototype.retrieveGenericSelectors = function(request) {
     // Cache looked-up low generic cosmetic filters.
     if (
         (simpleSelectors.size !== 0 || complexSelectors.size !== 0) &&
-        (typeof request.frameURL === 'string')
+        (typeof request.hostname === 'string') &&
+        (request.hostname !== '')
     ) {
-        var hostname = µb.URI.hostnameFromURI(request.frameURL);
-        if ( hostname !== '' ) {
-            this.addToSelectorCache({
-                selectors: out.simple.concat(out.complex),
-                type: 'cosmetic',
-                hostname: hostname,
-                cost: request.surveyCost || 0,
-            });
-        }
+        this.addToSelectorCache({
+            selectors: out.simple.concat(out.complex),
+            type: 'cosmetic',
+            hostname: request.hostname,
+            cost: request.surveyCost || 0,
+        });
     }
 
     // Important: always clear used registers before leaving.
@@ -2045,6 +2051,7 @@ FilterContainer.prototype.retrieveDomainSelectors = function(
 
     var r = {
         ready: this.frozen,
+        hostname: hostname,
         domain: domain,
         entity: entity,
         declarativeFilters: [],