diff --git a/esbuild/plugins.ts b/esbuild/plugins.ts
index b996be81..d65d2fc1 100644
--- a/esbuild/plugins.ts
+++ b/esbuild/plugins.ts
@@ -147,11 +147,6 @@ function processManifestPlugin({
           json.background = {
             scripts: [json.background.service_worker],
           };
-          json.content_scripts?.forEach((contentScript) => {
-            // TODO: Remove this when Firefox supports `world` - at least last 10
-            // versions
-            contentScript.world = undefined;
-          });
           delete json.minimum_chrome_version;
         } else {
           delete json['browser_specific_settings'];
diff --git a/src/background/services/background.ts b/src/background/services/background.ts
index d4e1ec03..885a6e20 100644
--- a/src/background/services/background.ts
+++ b/src/background/services/background.ts
@@ -51,6 +51,7 @@ export class Background {
 
   async start() {
     this.bindOnInstalled();
+    await this.injectPolyfill();
     await this.onStart();
     this.heartbeat.start();
     this.bindMessageHandler();
@@ -61,6 +62,35 @@ export class Background {
     this.sendToPopup.start();
   }
 
+  // TODO: When Firefox 128 is old enough, inject directly via manifest.
+  // Also see: injectPolyfill in contentScript
+  // See: https://github.com/interledger/web-monetization-extension/issues/607
+  async injectPolyfill() {
+    try {
+      await this.browser.scripting.registerContentScripts([
+        {
+          world: 'MAIN',
+          id: 'polyfill',
+          allFrames: true,
+          js: ['polyfill/polyfill.js'],
+          matches: PERMISSION_HOSTS.origins,
+          runAt: 'document_start',
+        },
+      ]);
+    } catch (error) {
+      // Firefox <128 will throw saying world: MAIN isn't supported. So, we'll
+      // inject via contentScript later. Injection via contentScript is slow,
+      // but apart from WM detection on page-load, everything else works fine.
+      if (!error.message.includes(`world`)) {
+        this.logger.error(
+          `Content script execution world \`MAIN\` not supported by your browser.\n` +
+            `Check https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting/ExecutionWorld#browser_compatibility for browser compatibility.`,
+          error,
+        );
+      }
+    }
+  }
+
   async onStart() {
     await this.storage.populate();
     await this.checkPermissions();
diff --git a/src/content/polyfill.ts b/src/content/polyfill.ts
index 062dae0d..ec12fd5c 100644
--- a/src/content/polyfill.ts
+++ b/src/content/polyfill.ts
@@ -1,5 +1,10 @@
 import type { MonetizationEventPayload } from '@/shared/messages';
 (function () {
+  if (document.createElement('link').relList.supports('monetization')) {
+    // already patched
+    return;
+  }
+
   const handlers = new WeakMap();
   const attributes: PropertyDescriptor & ThisType<EventTarget> = {
     enumerable: true,
diff --git a/src/content/services/contentScript.ts b/src/content/services/contentScript.ts
index 85466344..b5df9572 100644
--- a/src/content/services/contentScript.ts
+++ b/src/content/services/contentScript.ts
@@ -66,7 +66,9 @@ export class ContentScript {
   }
 
   // TODO: When Firefox has good support for `world: MAIN`, inject this directly
-  // via manifest.json https://bugzilla.mozilla.org/show_bug.cgi?id=1736575
+  // via manifest.json https://bugzilla.mozilla.org/show_bug.cgi?id=1736575 and
+  // remove this, along with injectPolyfill from background
+  // See: https://github.com/interledger/web-monetization-extension/issues/607
   async injectPolyfill() {
     const document = this.window.document;
     const script = document.createElement('script');
diff --git a/src/manifest.json b/src/manifest.json
index d8b29928..6680fd44 100644
--- a/src/manifest.json
+++ b/src/manifest.json
@@ -22,14 +22,14 @@
   "background": {
     "service_worker": "background/background.js"
   },
-  "permissions": ["tabs", "storage", "alarms"],
+  "permissions": ["tabs", "storage", "alarms", "scripting"],
   "action": {
     "default_title": "Web Monetization",
     "default_popup": "popup/index.html"
   },
   "web_accessible_resources": [
     {
-      "resources": ["assets/*", "polyfill/*"],
+      "resources": ["polyfill/*"],
       "matches": ["<all_urls>"]
     }
   ],