diff --git a/Makefile b/Makefile
index f7ce6b215..9c03018d5 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@ run_options := $(filter-out $@,$(MAKECMDGOALS))
 	compare maxcost medcost mincost modifiers record wasm
 
 sources := $(wildcard assets/* assets/*/* dist/version src/* src/*/* src/*/*/* src/*/*/*/*)
-platform := $(wildcard platform/* platform/*/* platform/*/*/* platform/*/*/*/*)
+platform := $(wildcard platform/* platform/*/* platform/*/*/* platform/*/*/*/* platform/*/*/*/*/*)
 assets := dist/build/uAssets
 
 all: chromium firefox npm
@@ -55,8 +55,11 @@ dig: dist/build/uBlock0.dig
 dig-snfe: dig
 	cd dist/build/uBlock0.dig && npm run snfe $(run_options)
 
-mv3: tools/make-mv3.sh $(sources) $(platform)
-	tools/make-mv3.sh
+mv3-chromium: tools/make-mv3.sh $(sources) $(platform)
+	tools/make-mv3.sh chromium
+
+mv3-firefox: tools/make-mv3.sh $(sources) $(platform)
+	tools/make-mv3.sh firefox
 
 mv3-quick: tools/make-mv3.sh $(sources) $(platform)
 	tools/make-mv3.sh quick
diff --git a/platform/mv3/extension/manifest.json b/platform/mv3/chromium/manifest.json
similarity index 100%
rename from platform/mv3/extension/manifest.json
rename to platform/mv3/chromium/manifest.json
diff --git a/platform/mv3/extension/js/background.js b/platform/mv3/extension/js/background.js
index 45a879af2..d2ab2c38f 100644
--- a/platform/mv3/extension/js/background.js
+++ b/platform/mv3/extension/js/background.js
@@ -169,7 +169,9 @@ async function onPermissionsRemoved() {
 
 function onMessage(request, sender, callback) {
 
-    if ( sender.origin !== UBOL_ORIGIN ) { return; }
+    // https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/MessageSender
+    //   Firefox API does not set `sender.origin`
+    if ( sender.origin !== undefined && sender.origin !== UBOL_ORIGIN ) { return; }
 
     switch ( request.what ) {
 
@@ -304,7 +306,11 @@ async function start() {
         console.log(`Available static rule count: ${count}`);
     });
 
-    dnr.setExtensionActionOptions({ displayActionCountAsBadgeText: true });
+    // https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/declarativeNetRequest
+    //   Firefox API does not support `dnr.setExtensionActionOptions`
+    if ( dnr.setExtensionActionOptions ) {
+        dnr.setExtensionActionOptions({ displayActionCountAsBadgeText: true });
+    }
 }
 
 (async ( ) => {
diff --git a/platform/mv3/extension/js/scripting-manager.js b/platform/mv3/extension/js/scripting-manager.js
index 16aaff374..c90b942a4 100644
--- a/platform/mv3/extension/js/scripting-manager.js
+++ b/platform/mv3/extension/js/scripting-manager.js
@@ -353,6 +353,10 @@ function registerDeclarative(context, declarativeDetails) {
 /******************************************************************************/
 
 function registerScriptlet(context, scriptletDetails) {
+    // https://bugzilla.mozilla.org/show_bug.cgi?id=1736575
+    //   `MAIN` world not yet supported in Firefox
+    if ( navigator && navigator.product === 'Gecko' ) { return; }
+
     const { before, filteringModeDetails, rulesetsDetails } = context;
 
     const hasBroadHostPermission =
@@ -427,6 +431,10 @@ function registerScriptlet(context, scriptletDetails) {
 /******************************************************************************/
 
 function registerScriptletEntity(context) {
+    // https://bugzilla.mozilla.org/show_bug.cgi?id=1736575
+    //   `MAIN` world not yet supported in Firefox
+    if ( navigator && navigator.product === 'Gecko' ) { return; }
+
     const { before, filteringModeDetails, rulesetsDetails } = context;
 
     const js = [];
diff --git a/platform/mv3/extension/js/scripting/css-declarative.js b/platform/mv3/extension/js/scripting/css-declarative.js
index 0f7d65d3f..b0d70f642 100644
--- a/platform/mv3/extension/js/scripting/css-declarative.js
+++ b/platform/mv3/extension/js/scripting/css-declarative.js
@@ -32,6 +32,7 @@
 /******************************************************************************/
 
 const declarativeImports = self.declarativeImports || [];
+delete self.declarativeImports;
 
 const lookupSelectors = (hn, out) => {
     for ( const { argsList, hostnamesMap } of declarativeImports ) {
diff --git a/platform/mv3/extension/js/scripting/css-generic.js b/platform/mv3/extension/js/scripting/css-generic.js
index dd78824d9..ad0169128 100644
--- a/platform/mv3/extension/js/scripting/css-generic.js
+++ b/platform/mv3/extension/js/scripting/css-generic.js
@@ -30,9 +30,9 @@
 (function uBOL_cssGeneric() {
 
 const genericSelectorMap = self.genericSelectorMap || new Map();
-if ( genericSelectorMap.size === 0 ) { return; }
+delete self.genericSelectorMap;
 
-self.genericSelectorMap = undefined;
+if ( genericSelectorMap.size === 0 ) { return; }
 
 /******************************************************************************/
 
diff --git a/platform/mv3/extension/js/scripting/css-procedural.js b/platform/mv3/extension/js/scripting/css-procedural.js
index f8fc6f0a1..4068023ba 100644
--- a/platform/mv3/extension/js/scripting/css-procedural.js
+++ b/platform/mv3/extension/js/scripting/css-procedural.js
@@ -659,6 +659,7 @@ class ProceduralFilterer {
 /******************************************************************************/
 
 const proceduralImports = self.proceduralImports || [];
+delete self.proceduralImports;
 
 const lookupSelectors = (hn, out) => {
     for ( const { argsList, hostnamesMap } of proceduralImports ) {
diff --git a/platform/mv3/extension/js/scripting/css-specific.entity.js b/platform/mv3/extension/js/scripting/css-specific.entity.js
index 9f4379533..9b38d31e6 100644
--- a/platform/mv3/extension/js/scripting/css-specific.entity.js
+++ b/platform/mv3/extension/js/scripting/css-specific.entity.js
@@ -34,6 +34,7 @@
 // $rulesetId$
 
 const specificEntityImports = self.specificEntityImports || [];
+delete self.specificEntityImports;
 
 /******************************************************************************/
 
@@ -65,8 +66,6 @@ for ( let i = 0; i < hnpartslen; i++ ) {
     }
 }
 
-self.specificEntityImports = undefined;
-
 if ( selectors.length === 0 ) { return; }
 
 try {
diff --git a/platform/mv3/firefox/background.html b/platform/mv3/firefox/background.html
new file mode 100644
index 000000000..58e9c5e17
--- /dev/null
+++ b/platform/mv3/firefox/background.html
@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>uBlock Origin Background Page</title>
+</head>
+<body>
+<script src="js/background.js" type="module"></script>
+</body>
+</html>
diff --git a/platform/mv3/firefox/manifest.json b/platform/mv3/firefox/manifest.json
new file mode 100644
index 000000000..fbe1d11f9
--- /dev/null
+++ b/platform/mv3/firefox/manifest.json
@@ -0,0 +1,48 @@
+{
+  "action": {
+    "default_icon": {
+      "16": "img/icon_16.png",
+      "32": "img/icon_32.png",
+      "64": "img/icon_64.png"
+    },
+    "default_popup": "popup.html"
+  },
+  "author": "Raymond Hill",
+  "background": {
+    "page": "background.html"
+  },
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "uBOLite@raymondhill.net",
+      "strict_min_version": "113a1"
+    }
+  },
+  "declarative_net_request": {
+    "rule_resources": [
+    ]
+  },
+  "default_locale": "en",
+  "description": "__MSG_extShortDesc__",
+  "icons": {
+    "16": "img/icon_16.png",
+    "32": "img/icon_32.png",
+    "64": "img/icon_64.png",
+    "128": "img/icon_128.png"
+  },
+  "manifest_version": 3,
+  "name": "__MSG_extName__",
+  "options_ui": {
+      "page": "dashboard.html"
+  },
+  "optional_permissions": [
+    "<all_urls>"
+  ],
+  "permissions": [
+    "activeTab",
+    "declarativeNetRequest",
+    "scripting"
+  ],
+  "short_name": "uBO Lite",
+  "version": "0.1",
+  "web_accessible_resources": []
+}
diff --git a/platform/mv3/make-rulesets.js b/platform/mv3/make-rulesets.js
index 45f256c22..5f632178e 100644
--- a/platform/mv3/make-rulesets.js
+++ b/platform/mv3/make-rulesets.js
@@ -1418,11 +1418,15 @@ async function main() {
     // Patch declarative_net_request key
     manifest.declarative_net_request = { rule_resources: ruleResources };
     // Patch web_accessible_resources key
-    manifest.web_accessible_resources = [{
+    const web_accessible_resources = {
         resources: Array.from(requiredRedirectResources).map(path => `/${path}`),
         matches: [ '<all_urls>' ],
-        use_dynamic_url: true,
-    }];
+    };
+    if ( commandLineArgs.get('platform') === 'chromium' ) {
+        web_accessible_resources.use_dynamic_url = true;
+    }
+    manifest.web_accessible_resources = [ web_accessible_resources ];
+
     // Patch version key
     const now = new Date();
     const yearPart = now.getUTCFullYear() - 2000;
diff --git a/tools/make-mv3.sh b/tools/make-mv3.sh
index 20f631583..cfaf8b396 100755
--- a/tools/make-mv3.sh
+++ b/tools/make-mv3.sh
@@ -6,12 +6,32 @@ set -e
 
 echo "*** uBOLite.mv3: Creating extension"
 
-DES="dist/build/uBOLite.mv3"
+PLATFORM="chromium"
 
-if [ "$1" != "quick" ]; then
+for i in "$@"; do
+  case $i in
+    quick)
+      QUICK="yes"
+      shift # past argument=value
+      ;;
+    firefox)
+      PLATFORM="firefox"
+      shift # past argument=value
+      ;;
+    chromium)
+      PLATFORM="chromium"
+      shift # past argument=value
+      ;;
+  esac
+done
+
+DES="dist/build/uBOLite.$PLATFORM"
+
+if [ "$QUICK" != "yes" ]; then
     rm -rf $DES
 fi
 
+
 mkdir -p $DES
 cd $DES
 DES=$(pwd)
@@ -35,17 +55,24 @@ cp src/js/i18n.js $DES/js/
 cp LICENSE.txt $DES/
 
 echo "*** uBOLite.mv3: Copying mv3-specific files"
+if [ "$PLATFORM" = "firefox" ]; then
+    cp platform/mv3/firefox/background.html $DES/
+fi
 cp platform/mv3/extension/*.html $DES/
 cp platform/mv3/extension/css/* $DES/css/
 cp -R platform/mv3/extension/js/* $DES/js/
 cp platform/mv3/extension/img/* $DES/img/
 cp -R platform/mv3/extension/_locales $DES/
 
-if [ "$1" != "quick" ]; then
+if [ "$QUICK" != "yes" ]; then
     echo "*** uBOLite.mv3: Generating rulesets"
     TMPDIR=$(mktemp -d)
     mkdir -p $TMPDIR
-    cp platform/mv3/extension/manifest.json $DES/
+    if [ "$PLATFORM" = "chromium" ]; then
+        cp platform/mv3/chromium/manifest.json $DES/
+    elif [ "$PLATFORM" = "firefox" ]; then
+        cp platform/mv3/firefox/manifest.json $DES/
+    fi
     ./tools/make-nodejs.sh $TMPDIR
     cp platform/mv3/package.json $TMPDIR/
     cp platform/mv3/*.js $TMPDIR/
@@ -55,7 +82,7 @@ if [ "$1" != "quick" ]; then
     mkdir -p $TMPDIR/web_accessible_resources
     cp src/web_accessible_resources/* $TMPDIR/web_accessible_resources/
     cd $TMPDIR
-    node --no-warnings make-rulesets.js output=$DES
+    node --no-warnings make-rulesets.js output=$DES platform="$PLATFORM"
     cd - > /dev/null
     rm -rf $TMPDIR
 fi