Try to inject scriptlets at onResponseStarted() time

Related issue:
- uBlockOrigin/uBlock-issues#2350

As per AdGuard findings, it's possible (though unreliable) to try
to inject scriptlets at webRequest.onResponseStarted time, which
increases scriptlet injection reliability overall when injecting
from multiple entry points.

uBO was already injecting at webNavigation.onCommitted and
main content script time, and adding webRequest.onResponseStarted
as an entry point for scriptlet injection increases reliability
for webpages which executes inline scripts at the top of the DOM.

References:
- AdguardTeam/AdguardBrowserExtension#1029
- https://github.com/AdguardTeam/AdguardBrowserExtension/blob/9ab85be5/Extension/src/background/webrequest.js#L620

src/js/scriptlet-filtering.js

@@ -96,7 +96,6 @@ const contentscriptCode = (( ) => {
             ) {
                 return;
             }
-            self.uBO_scriptletsInjected = true;
             const injectScriptlets = function(d) {
                 let script;
                 try {
@@ -105,12 +104,11 @@ const contentscriptCode = (( ) => {
                         decodeURIComponent(scriptlets))
                     );
                     (d.head || d.documentElement).appendChild(script);
+                    self.uBO_scriptletsInjected = true;
                 } catch (ex) {
                 }
                 if ( script ) {
-                    if ( script.parentNode ) {
-                        script.parentNode.removeChild(script);
-                    }
+                    script.remove();
                     script.textContent = '';
                 }
             };

src/js/start.js

@@ -19,6 +19,8 @@
     Home: https://github.com/gorhill/uBlock
 */
 
+/* globals browser */
+
 'use strict';
 
 /******************************************************************************/

src/js/tab.js

@@ -933,10 +933,7 @@ vAPI.Tabs = class extends vAPI.Tabs {
         const pageStore = µb.pageStoreFromTabId(tabId);
         if ( pageStore === null ) { return; }
         pageStore.setFrameURL(details);
-        if (
-            vAPI.webextFlavor.soup.has('firefox') === false &&
-            pageStore.getNetFilteringSwitch()
-        ) {
+        if ( pageStore.getNetFilteringSwitch() ) {
             scriptletFilteringEngine.injectNow(details);
         }
     }

src/js/traffic.js

@@ -19,6 +19,8 @@
     Home: https://github.com/gorhill/uBlock
 */
 
+/* globals browser */
+
 'use strict';
 
 /******************************************************************************/
@@ -1131,6 +1133,11 @@ const strictBlockBypasser = {
 
 /******************************************************************************/
 
+// https://github.com/uBlockOrigin/uBlock-issues/issues/2350
+//   Added scriptlet injection attempt at onResponseStarted time as per
+//   https://github.com/AdguardTeam/AdguardBrowserExtension/issues/1029 and
+//   https://github.com/AdguardTeam/AdguardBrowserExtension/blob/9ab85be5/Extension/src/background/webrequest.js#L620
+
 const webRequest = {
     onBeforeRequest,
 
@@ -1148,6 +1155,19 @@ const webRequest = {
                 { urls: [ 'http://*/*', 'https://*/*' ] },
                 [ 'blocking', 'responseHeaders' ]
             );
+            vAPI.net.addListener(
+                'onResponseStarted',
+                details => {
+                    const pageStore = µb.pageStoreFromTabId(details.tabId);
+                    if ( pageStore === null ) { return; }
+                    if ( pageStore.getNetFilteringSwitch() === false ) { return; }
+                    scriptletFilteringEngine.injectNow(details);
+                },
+                {
+                    types: [ 'main_frame', 'sub_frame' ],
+                    urls: [ 'http://*/*', 'https://*/*' ]
+                }
+            );
             vAPI.net.unsuspend({ all: true });
         };
     })(),