diff --git a/src/background.html b/src/background.html
index 7edea355e..4565a2778 100644
--- a/src/background.html
+++ b/src/background.html
@@ -15,6 +15,7 @@
 <script src="js/async.js"></script>
 <script src="js/liquid-dict.js"></script>
 <script src="js/utils.js"></script>
+<script src="js/uritools.js"></script>
 <script src="js/assets.js"></script>
 <script src="js/dynamic-net-filtering.js"></script>
 <script src="js/static-net-filtering.js"></script>
@@ -24,7 +25,6 @@
 <script src="js/profiler.js"></script>
 <script src="js/storage.js"></script>
 <script src="js/pagestore.js"></script>
-<script src="js/uritools.js"></script>
 <script src="js/tab.js"></script>
 <script src="js/traffic.js"></script>
 <script src="js/contextmenu.js"></script>
diff --git a/src/js/dynamic-net-filtering.js b/src/js/dynamic-net-filtering.js
index 53d9885b6..c899ece3f 100644
--- a/src/js/dynamic-net-filtering.js
+++ b/src/js/dynamic-net-filtering.js
@@ -194,25 +194,24 @@ Matrix.prototype.evaluateCell = function(srcHostname, desHostname, type) {
 
 Matrix.prototype.clearRegisters = function() {
     this.r = 0;
-    this.type = '';
-    this.y = '';
-    this.z = '';
+    this.type = this.y = this.z = '';
     return this;
 };
 
 /******************************************************************************/
 
-var isFirstParty = function(srcHostname, desHostname) {
-    if ( desHostname.slice(0 - srcHostname.length) !== srcHostname ) {
-        return false;
-    }
-    // Be sure to not confuse 'example.com' with 'anotherexample.com'
-    if ( desHostname.lenght === srcHostname.lenght ) {
+var is3rdParty = function(srcHostname, desHostname) {
+    var srcDomain = domainFromHostname(srcHostname);
+    if ( desHostname.slice(0 - srcDomain.length) !== srcDomain ) {
         return true;
     }
-    return desHostname.charAt(desHostname.length - srcHostname.length - 1) === '.';
+    // Do not confuse 'example.com' with 'anotherexample.com'
+    return desHostname.lenght !== srcDomain.lenght &&
+           desHostname.charAt(desHostname.length - srcDomain.length - 1) !== '.';
 };
 
+var domainFromHostname = µBlock.URI.domainFromHostname;
+
 /******************************************************************************/
 
 Matrix.prototype.evaluateCellZ = function(srcHostname, desHostname, type) {
@@ -262,20 +261,18 @@ Matrix.prototype.evaluateCellZY = function(srcHostname, desHostname, type) {
     this.y = '*';
 
     if ( type === 'script' ) {
-        type = isFirstParty(srcHostname, desHostname) ? '1p-script' : '3p-script';
-    } else if ( type === 'sub_frame' && isFirstParty(srcHostname, desHostname) === false ) {
+        type = is3rdParty(srcHostname, desHostname) ? '3p-script' : '1p-script';
+    } else if ( type === 'sub_frame' && is3rdParty(srcHostname, desHostname) ) {
         type = '3p-frame';
     }
-
     // Is this a type suitable for dynamic filtering purpose?
-    if ( supportedDynamicTypes.hasOwnProperty(type) === false ) {
-        this.type = '';
-        return this;
+    if ( supportedDynamicTypes.hasOwnProperty(type) ) {
+        this.type = type;
+        this.r = this.evaluateCellZ(srcHostname, '*', type);
+        if ( this.r !== 0 ) { return this; }
     }
 
-    this.type = type;
-    this.r = this.evaluateCellZ(srcHostname, '*', type);
-
+    this.type = '';
     return this;
 };
 
diff --git a/src/js/messaging.js b/src/js/messaging.js
index 90ec132d4..fe19ef1b2 100644
--- a/src/js/messaging.js
+++ b/src/js/messaging.js
@@ -109,7 +109,7 @@ var µb = µBlock;
 
 var getHostnameDict = function(hostnameToCountMap) {
     var r = {};
-    var µburi = µb.URI;
+    var domainFromHostname = µb.URI.domainFromHostname;
     var domain, counts;
     for ( var hostname in hostnameToCountMap ) {
         if ( hostnameToCountMap.hasOwnProperty(hostname) === false ) {
@@ -118,7 +118,7 @@ var getHostnameDict = function(hostnameToCountMap) {
         if ( r.hasOwnProperty(hostname) ) {
             continue;
         }
-        domain = µburi.domainFromHostname(hostname);
+        domain = domainFromHostname(hostname);
         counts = hostnameToCountMap[domain] || 0;
         r[domain] = {
             domain: domain,
diff --git a/src/js/uritools.js b/src/js/uritools.js
index 5e37bd52f..45065fbc1 100644
--- a/src/js/uritools.js
+++ b/src/js/uritools.js
@@ -274,21 +274,98 @@ URI.hostnameFromURI = function(uri) {
 
 /******************************************************************************/
 
-// It is expected that there is higher-scoped `publicSuffixList` lingering
-// somewhere. Cache it. See <https://github.com/gorhill/publicsuffixlist.js>.
-var psl = publicSuffixList;
-
 URI.domainFromHostname = function(hostname) {
-    if ( !reIPAddressNaive.test(hostname) ) {
-        return psl.getDomain(hostname);
+    // Try to skip looking up the PSL database
+    if ( domainCache.hasOwnProperty(hostname) ) {
+        var entry = domainCache[hostname];
+        entry.tstamp = Date.now();
+        return entry.domain;
     }
-    return hostname;
+    // Meh.. will have to search it
+    if ( reIPAddressNaive.test(hostname) === false ) {
+        return domainCacheAdd(hostname, psl.getDomain(hostname));
+    }
+    return domainCacheAdd(hostname, hostname);
 };
 
 URI.domain = function() {
     return this.domainFromHostname(this.hostname);
 };
 
+// It is expected that there is higher-scoped `publicSuffixList` lingering
+// somewhere. Cache it. See <https://github.com/gorhill/publicsuffixlist.js>.
+var psl = publicSuffixList;
+
+/******************************************************************************/
+
+// Trying to alleviate the worries of looking up too often the domain name from
+// a hostname. With a cache, uBlock benefits given that it deals with a
+// specific set of hostnames within a narrow time span -- in other words, I
+// believe probability of cache hit are high in uBlock.
+
+var DomainCacheEntry = function(domain) {
+    this.init(domain);
+};
+
+DomainCacheEntry.prototype.init = function(domain) {
+    this.domain = domain;
+    this.tstamp = Date.now();
+    return this;
+};
+
+DomainCacheEntry.prototype.dispose = function() {
+    this.domain = '';
+    if ( domainCacheEntryJunkyard.length < 25 ) {
+        domainCacheEntryJunkyard.push(this);
+    }
+};
+
+var domainCacheEntryFactory = function(domain) {
+    var entry = domainCacheEntryJunkyard.pop();
+    if ( entry ) {
+        return entry.init(domain);
+    }
+    return new DomainCacheEntry(domain);
+};
+
+var domainCacheEntryJunkyard = [];
+
+var domainCacheAdd = function(hostname, domain) {
+    if ( domainCache.hasOwnProperty(hostname) ) {
+        domainCache[hostname].tstamp = Date.now();
+    } else {
+        domainCache[hostname] = domainCacheEntryFactory(domain);
+        domainCacheCount += 1;
+        if ( domainCacheCount === domainCacheCountHighWaterMark ) {
+            domainCachePrune();
+        }
+    }
+    return domain;
+};
+
+var domainCacheEntrySort = function(a, b) {
+    return b.tstamp - a.tstamp;
+};
+
+var domainCachePrune = function() {
+    var hostnames = Object.keys(domainCache)
+                          .sort(domainCacheEntrySort)
+                          .slice(domainCacheCountLowWaterMark);
+    var i = hostnames.length;
+    domainCacheCount -= i;
+    var hostname;
+    while ( i-- ) {
+        hostname = hostnames[i];
+        domainCache[hostname].dispose();
+        delete domainCache[hostname];
+    }
+};
+
+var domainCache = {};
+var domainCacheCount = 0;
+var domainCacheCountLowWaterMark = 75;
+var domainCacheCountHighWaterMark = 100;
+
 /******************************************************************************/
 
 URI.domainFromURI = function(uri) {