diff --git a/platform/mv3/extension/js/scripting-manager.js b/platform/mv3/extension/js/scripting-manager.js
index f1f949016..9a99c2929 100644
--- a/platform/mv3/extension/js/scripting-manager.js
+++ b/platform/mv3/extension/js/scripting-manager.js
@@ -417,10 +417,6 @@ function registerSpecific(context) {
 /******************************************************************************/
 
 function registerScriptlet(context, scriptletDetails) {
-    // https://bugzilla.mozilla.org/show_bug.cgi?id=1736575
-    //   `MAIN` world not yet supported in Firefox
-    if ( isGecko ) { return; }
-
     const { before, filteringModeDetails, rulesetsDetails } = context;
 
     const hasBroadHostPermission =
@@ -476,9 +472,14 @@ function registerScriptlet(context, scriptletDetails) {
                 matches,
                 excludeMatches,
                 runAt: 'document_start',
-                world: 'MAIN',
             };
 
+            // https://bugzilla.mozilla.org/show_bug.cgi?id=1736575
+            //   `MAIN` world not yet supported in Firefox
+            if ( isGecko === false ) {
+                directive.world = 'MAIN';
+            }
+
             // register
             if ( registered === undefined ) {
                 context.toAdd.push(directive);
diff --git a/platform/mv3/extension/js/scripting/css-procedural.js b/platform/mv3/extension/js/scripting/css-procedural.js
index 388f1c822..5c477f1d1 100644
--- a/platform/mv3/extension/js/scripting/css-procedural.js
+++ b/platform/mv3/extension/js/scripting/css-procedural.js
@@ -485,8 +485,13 @@ class PSelector {
     prime(input) {
         const root = input || document;
         if ( this.selector === '' ) { return [ root ]; }
-        if ( input !== document && /^ [>+~]/.test(this.selector) ) {
-            return Array.from(PSelectorSpathTask.qsa(input, this.selector));
+        if ( input !== document ) {
+            const c0 = this.selector.charCodeAt(0);
+            if ( c0 === 0x2B /* + */ || c0 === 0x7E /* ~ */ ) {
+                return Array.from(PSelectorSpathTask.qsa(input, this.selector));
+            } else if ( c0 === 0x3E /* > */ ) {
+                return Array.from(input.querySelectorAll(`:scope ${this.selector}`));
+            }
         }
         return Array.from(root.querySelectorAll(this.selector));
     }
diff --git a/platform/mv3/make-rulesets.js b/platform/mv3/make-rulesets.js
index 5f95b6c51..0972c62e7 100644
--- a/platform/mv3/make-rulesets.js
+++ b/platform/mv3/make-rulesets.js
@@ -53,19 +53,23 @@ const commandLineArgs = (( ) => {
     return args;
 })();
 
+const platform = commandLineArgs.get('platform') || 'chromium';
 const outputDir = commandLineArgs.get('output') || '.';
 const cacheDir = `${outputDir}/../mv3-data`;
 const rulesetDir = `${outputDir}/rulesets`;
 const scriptletDir = `${rulesetDir}/scripting`;
 const env = [
-    'chromium',
+    platform,
     'mv3',
-    'native_css_has',
     'ublock',
     'ubol',
     'user_stylesheet',
 ];
 
+if ( platform !== 'firefox' ) {
+    env.push('native_css_has');
+}
+
 /******************************************************************************/
 
 const jsonSetMapReplacer = (k, v) => {
@@ -1222,7 +1226,7 @@ async function main() {
         resources: Array.from(requiredRedirectResources).map(path => `/${path}`),
         matches: [ '<all_urls>' ],
     };
-    if ( commandLineArgs.get('platform') === 'chromium' ) {
+    if ( platform === 'chromium' ) {
         web_accessible_resources.use_dynamic_url = true;
     }
     manifest.web_accessible_resources = [ web_accessible_resources ];
diff --git a/platform/mv3/make-scriptlets.js b/platform/mv3/make-scriptlets.js
index 63cf9f27f..2bc920d07 100644
--- a/platform/mv3/make-scriptlets.js
+++ b/platform/mv3/make-scriptlets.js
@@ -167,7 +167,7 @@ export async function commit(rulesetId, path, writeFn) {
         content = safeReplace(content, /\$scriptletName\$/, details.name, 0);
         content = safeReplace(content,
             'self.$argsList$',
-            JSON.stringify(Array.from(details.args.keys()))
+            JSON.stringify(Array.from(details.args.keys()).map(a => JSON.parse(a)))
         );
         content = safeReplace(content,
             'self.$hostnamesMap$',
diff --git a/platform/mv3/scriptlets/scriptlet.template.js b/platform/mv3/scriptlets/scriptlet.template.js
index b6859f5af..f6ade44f2 100644
--- a/platform/mv3/scriptlets/scriptlet.template.js
+++ b/platform/mv3/scriptlets/scriptlet.template.js
@@ -21,6 +21,7 @@
 */
 
 /* jshint esversion:11 */
+/* global cloneInto */
 
 'use strict';
 
@@ -31,10 +32,14 @@
 // Important!
 // Isolate from global scope
 
-(function uBOL_$scriptletName$() {
+// Start of local scope
+(( ) => {
 
 /******************************************************************************/
 
+// Start of injected code
+const uBOL_$scriptletName$ = function() {
+
 const scriptletGlobals = new Map(); // jshint ignore: line
 
 const argsList = self.$argsList$;
@@ -109,13 +114,58 @@ if ( entitiesMap.size !== 0 ) {
 
 // Apply scriplets
 for ( const i of todoIndices ) {
-    try { $scriptletName$(...JSON.parse(argsList[i])); }
+    try { $scriptletName$(...argsList[i]); }
     catch(ex) {}
 }
 argsList.length = 0;
 
 /******************************************************************************/
 
+};
+// End of injected code
+
+/******************************************************************************/
+
+// Inject code
+
+// https://bugzilla.mozilla.org/show_bug.cgi?id=1736575
+//   `MAIN` world not yet supported in Firefox, so we inject the code into
+//   'MAIN' ourself when enviroment in Firefox.
+
+// Not Firefox
+if ( typeof wrappedJSObject !== 'object' ) {
+    return uBOL_$scriptletName$();
+}
+
+// Firefox
+{
+    const page = self.wrappedJSObject;
+    let script, url;
+    try {
+        page.uBOL_$scriptletName$ = cloneInto([
+            [ '(', uBOL_$scriptletName$.toString(), ')();' ],
+            { type: 'text/javascript; charset=utf-8' },
+        ], self);
+        const blob = new page.Blob(...page.uBOL_$scriptletName$);
+        url = page.URL.createObjectURL(blob);
+        const doc = page.document;
+        script = doc.createElement('script');
+        script.async = false;
+        script.src = url;
+        (doc.head || doc.documentElement || doc).append(script);
+    } catch (ex) {
+        console.error(ex);
+    }
+    if ( url ) {
+        if ( script ) { script.remove(); }
+        page.URL.revokeObjectURL(url);
+    }
+    delete page.uBOL_$scriptletName$;
+}
+
+/******************************************************************************/
+
+// End of local scope
 })();
 
 /******************************************************************************/
diff --git a/src/js/contentscript-extra.js b/src/js/contentscript-extra.js
index 29a736d21..88d9f1349 100644
--- a/src/js/contentscript-extra.js
+++ b/src/js/contentscript-extra.js
@@ -378,8 +378,13 @@ class PSelector {
     prime(input) {
         const root = input || document;
         if ( this.selector === '' ) { return [ root ]; }
-        if ( input !== document && /^ ?[>+~]/.test(this.selector) ) {
-            return Array.from(PSelectorSpathTask.qsa(input, this.selector));
+        if ( input !== document ) {
+            const c0 = this.selector.charCodeAt(0);
+            if ( c0 === 0x2B /* + */ || c0 === 0x7E /* ~ */ ) {
+                return Array.from(PSelectorSpathTask.qsa(input, this.selector));
+            } else if ( c0 === 0x3E /* > */ ) {
+                return Array.from(input.querySelectorAll(`:scope ${this.selector}`));
+            }
         }
         return Array.from(root.querySelectorAll(this.selector));
     }
diff --git a/tools/make-mv3.sh b/tools/make-mv3.sh
index a4e46e29e..353ff8d0e 100755
--- a/tools/make-mv3.sh
+++ b/tools/make-mv3.sh
@@ -35,7 +35,6 @@ if [ "$QUICK" != "yes" ]; then
     rm -rf $DES
 fi
 
-
 mkdir -p $DES
 cd $DES
 DES=$(pwd)
@@ -45,11 +44,15 @@ mkdir -p $DES/css/fonts
 mkdir -p $DES/js
 mkdir -p $DES/img
 
-UBO_DIR=$(mktemp -d)
-UBO_REPO="https://github.com/gorhill/uBlock.git"
-UBO_VERSION=$(cat platform/mv3/ubo-version)
-echo "*** uBOLite.mv3: Fetching uBO $UBO_VERSION from $UBO_REPO into $UBO_DIR"
-git clone -q --depth 1 --branch "$UBO_VERSION" "$UBO_REPO" "$UBO_DIR"
+if [ "$UBO_VERSION" != "local" ]; then
+    UBO_VERSION=$(cat platform/mv3/ubo-version)
+    UBO_REPO="https://github.com/gorhill/uBlock.git"
+    UBO_DIR=$(mktemp -d)
+    echo "*** uBOLite.mv3: Fetching uBO $UBO_VERSION from $UBO_REPO into $UBO_DIR"
+    git clone -q --depth 1 --branch "$UBO_VERSION" "$UBO_REPO" "$UBO_DIR"
+else
+    UBO_DIR=.
+fi
 
 echo "*** uBOLite.mv3: Copying common files"
 cp -R $UBO_DIR/src/css/fonts/* $DES/css/fonts/