diff --git a/src/js/cosmetic-filtering.js b/src/js/cosmetic-filtering.js
index 9f738fa05..939f6314f 100644
--- a/src/js/cosmetic-filtering.js
+++ b/src/js/cosmetic-filtering.js
@@ -665,6 +665,7 @@ var FilterContainer = function() {
     };
 
     this.userScripts = new Map();
+    this.userScriptCache = new µb.MRUCache(32);
 
     // Short-lived: content is valid only during one function call. These
     // is to prevent repeated allocation/deallocation overheads -- the
@@ -722,7 +723,9 @@ FilterContainer.prototype.reset = function() {
 
     this.scriptTagFilters = {};
     this.scriptTagFilterCount = 0;
+
     this.userScripts.clear();
+    this.userScriptCache.reset();
 };
 
 /******************************************************************************/
@@ -1734,19 +1737,26 @@ FilterContainer.prototype.retrieveUserScripts = function(
 
 FilterContainer.prototype._lookupUserScript = function(raw, reng, toInject) {
     if ( toInject.has(raw) ) { return; }
-    var token, args,
-        pos = raw.indexOf(',');
-    if ( pos === -1 ) {
-        token = raw;
-    } else {
-        token = raw.slice(0, pos).trim();
-        args = raw.slice(pos + 1).trim();
+    if ( this.userScriptCache.resetTime < reng.modifyTime ) {
+        this.userScriptCache.reset();
     }
-    var content = reng.resourceContentFromName(token, 'application/javascript');
-    if ( !content ) { return; }
-    if ( args ) {
-        content = this._fillupUserScript(content, args);
+    var content = this.userScriptCache.lookup(raw);
+    if ( content === undefined ) {
+        var token, args,
+            pos = raw.indexOf(',');
+        if ( pos === -1 ) {
+            token = raw;
+        } else {
+            token = raw.slice(0, pos).trim();
+            args = raw.slice(pos + 1).trim();
+        }
+        content = reng.resourceContentFromName(token, 'application/javascript');
         if ( !content ) { return; }
+        if ( args ) {
+            content = this._fillupUserScript(content, args);
+            if ( !content ) { return; }
+        }
+        this.userScriptCache.add(raw, content);
     }
     toInject.set(raw, content);
 };
diff --git a/src/js/redirect-engine.js b/src/js/redirect-engine.js
index 70912195a..47efae2a1 100644
--- a/src/js/redirect-engine.js
+++ b/src/js/redirect-engine.js
@@ -1,7 +1,7 @@
 /*******************************************************************************
 
     uBlock Origin - a browser extension to block requests.
-    Copyright (C) 2015-2016 Raymond Hill
+    Copyright (C) 2015-2017 Raymond Hill
 
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -95,6 +95,7 @@ RedirectEngine.prototype.reset = function() {
     this.ruleTypes = new Set();
     this.ruleSources = new Set();
     this.ruleDestinations = new Set();
+    this.modifyTime = Date.now();
 };
 
 /******************************************************************************/
@@ -189,6 +190,7 @@ RedirectEngine.prototype.addRule = function(src, des, type, pattern, redirect) {
         entries = this.rules.get(key);
     if ( entries === undefined ) {
         this.rules.set(key, [ { tok: redirect, pat: pattern } ]);
+        this.modifyTime = Date.now();
         return;
     }
     var entry;
@@ -363,6 +365,7 @@ RedirectEngine.prototype.fromSelfie = function(selfie) {
     this.ruleTypes = new Set(selfie.ruleTypes);
     this.ruleSources = new Set(selfie.ruleSources);
     this.ruleDestinations = new Set(selfie.ruleDestinations);
+    this.modifyTime = Date.now();
 
     return true;
 };
diff --git a/src/js/utils.js b/src/js/utils.js
index fdde0d3ec..970b72fe9 100644
--- a/src/js/utils.js
+++ b/src/js/utils.js
@@ -351,6 +351,7 @@
     this.size = size;
     this.array = [];
     this.map = new Map();
+    this.resetTime = Date.now();
 };
 
 µBlock.MRUCache.prototype = {
@@ -380,6 +381,7 @@
     reset: function() {
         this.array = [];
         this.map.clear();
+        this.resetTime = Date.now();
     }
 };