Fix #3069, and consequently #3374, #3378.

A new filtering class has been created: "static extended filtering".
This new class is an umbrella class for more specialized filtering
engines:
- Cosmetic filtering
- Scriptlet filtering
- HTML filtering

HTML filtering is available only on platforms which support modifying
the response body on the fly, so only Firefox 57+ at the moment.

With the ability to modify the response body, HTML filtering has
been introduced: removing elements from the DOM before the source
data has been parsed by the browser.

A consequence of HTML filtering ability is to bring back script tag
filtering feature.

platform/webext/vapi-webrequest.js

@@ -29,7 +29,11 @@ vAPI.net = {
     onBeforeRequest: {},
     onBeforeMaybeSpuriousCSPReport: {},
     onHeadersReceived: {},
-    nativeCSPReportFiltering: true
+    nativeCSPReportFiltering: true,
+    webRequest: browser.webRequest,
+    canFilterResponseBody:
+        typeof browser.webRequest === 'object' &&
+        typeof browser.webRequest.filterResponseData === 'function'
 };
 
 /******************************************************************************/

src/background.html

@@ -22,7 +22,10 @@
 <script src="js/dynamic-net-filtering.js"></script>
 <script src="js/static-net-filtering.js"></script>
 <script src="js/url-net-filtering.js"></script>
+<script src="js/static-ext-filtering.js"></script>
 <script src="js/cosmetic-filtering.js"></script>
+<script src="js/scriptlet-filtering.js"></script>
+<script src="js/html-filtering.js"></script>
 <script src="js/hnswitches.js"></script>
 <script src="js/ublock.js"></script>
 <script src="js/messaging.js"></script>

src/js/assets.js

@@ -53,11 +53,10 @@ api.removeObserver = function(observer) {
 };
 
 var fireNotification = function(topic, details) {
-    var result;
+    var result, r;
     for ( var i = 0; i < observers.length; i++ ) {
-        if ( observers[i](topic, details) === false ) {
-            result = false;
-        }
+        r = observers[i](topic, details);
+        if ( r !== undefined ) { result = r; }
     }
     return result;
 };
@@ -955,7 +954,7 @@ var updateNext = function() {
                 fireNotification(
                     'before-asset-updated',
                     { assetKey: assetKey,  type: assetEntry.content }
-                ) !== false
+                ) === true
             ) {
                 return assetKey;
             }

src/js/background.js

@@ -95,6 +95,7 @@ var µBlock = (function() { // jshint ignore:line
         // Features detection.
         privacySettingsSupported: vAPI.browserSettings instanceof Object,
         cloudStorageSupported: vAPI.cloud instanceof Object,
+        canFilterResponseBody: vAPI.net.canFilterResponseBody === true,
 
         // https://github.com/chrisaljoudi/uBlock/issues/180
         // Whitelist directives need to be loaded once the PSL is available
@@ -120,8 +121,8 @@ var µBlock = (function() { // jshint ignore:line
 
         // read-only
         systemSettings: {
-            compiledMagic: 'vrgorlgelgws',
-            selfieMagic: 'pxpclstriajk'
+            compiledMagic: 'puuijtkfpspv',
+            selfieMagic: 'puuijtkfpspv'
         },
 
         restoreBackupSettings: {

src/js/contentscript.js

@@ -1379,20 +1379,9 @@ vAPI.domSurveyor = (function() {
 
         // Library of resources is located at:
         // https://github.com/gorhill/uBlock/blob/master/assets/ublock/resources.txt
-        if ( cfeDetails.scripts ) {
-            // Have the injected script tag remove itself when execution completes:
-            // to keep DOM as clean as possible.
-            var text = cfeDetails.scripts +
-                "\n" +
-                "(function() {\n" +
-                "    var c = document.currentScript,\n" +
-                "        p = c && c.parentNode;\n" +
-                "    if ( p ) {\n" +
-                "        p.removeChild(c);\n" +
-                "    }\n" +
-                "})();";
-            vAPI.injectScriptlet(document, text);
-            vAPI.injectedScripts = text;
+        if ( response.scriptlets ) {
+            vAPI.injectScriptlet(document, response.scriptlets);
+            vAPI.injectedScripts = response.scriptlets;
         }
 
         if ( vAPI.domSurveyor instanceof Object ) {
@@ -1414,13 +1403,11 @@ vAPI.domSurveyor = (function() {
     };
 
     // This starts bootstrap process.
-    var url = window.location.href;
     vAPI.messaging.send(
         'contentscript',
         {
             what: 'retrieveContentScriptParameters',
-            pageURL: url,
-            locationURL: url,
+            url: window.location.href,
             isRootFrame: window === window.top
         },
         bootstrapPhase1