diff --git a/firefox/manifest.json b/firefox/manifest.json
index 6d92013..e738e6e 100644
--- a/firefox/manifest.json
+++ b/firefox/manifest.json
@@ -15,7 +15,7 @@
       }
     }
   },
-  "permissions": ["alarms", "contextMenus", "idle", "storage", "tabs", "windows", "http://127.0.0.1/*", "http://localhost/*"],
+  "permissions": ["alarms", "contextMenus", "idle", "storage", "tabs", "http://127.0.0.1/*", "http://localhost/*"],
   "background": {
     "scripts": ["hostname.js", "activity-tracker.js", "protocol.js", "api.js", "queue.js", "i18n.js", "background.js"]
   },
diff --git a/package.json b/package.json
index 7a0bb90..8dd403e 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,7 @@
   "license": "AGPL-3.0-or-later",
   "scripts": {
     "build": "node scripts/build-extension.js",
-    "test": "node scripts/test-hostname.js && node scripts/test-activity-tracker.js && node scripts/test-protocol.js && node scripts/test-i18n.js && node scripts/test-popup-settings.js && node scripts/test-popup-select-style.js && node scripts/test-popup-catalog-fallback.js && node scripts/test-background-i18n.js && node scripts/test-firefox-github-release.js",
+    "test": "node scripts/test-manifests.js && node scripts/test-hostname.js && node scripts/test-activity-tracker.js && node scripts/test-protocol.js && node scripts/test-i18n.js && node scripts/test-popup-settings.js && node scripts/test-popup-select-style.js && node scripts/test-popup-catalog-fallback.js && node scripts/test-background-i18n.js && node scripts/test-firefox-github-release.js",
     "sign:firefox": "./scripts/sign-firefox-xpi.sh",
     "release:firefox": "./scripts/release-firefox-xpi.sh",
     "publish:firefox": "./scripts/publish-firefox-github-release.sh",
diff --git a/scripts/test-manifests.js b/scripts/test-manifests.js
new file mode 100644
index 0000000..7e351f4
--- /dev/null
+++ b/scripts/test-manifests.js
@@ -0,0 +1,15 @@
+#!/usr/bin/env node
+const assert = require('assert');
+
+const chromium = require('../chromium/manifest.json');
+const firefox = require('../firefox/manifest.json');
+
+assert.equal(chromium.version, firefox.version, 'browser packages must use the same version');
+assert.equal(
+  firefox.permissions.includes('windows'),
+  false,
+  'Firefox does not accept the Chromium-only windows permission'
+);
+assert.equal(chromium.permissions.includes('windows'), true, 'Chromium still needs the windows permission');
+
+console.log('browser manifest compatibility tests passed');