diff --git a/README.md b/README.md
index d5e45c7..113a6cc 100644
--- a/README.md
+++ b/README.md
@@ -13,13 +13,15 @@ to your browser.
 
 ## Install
 
+**Chrome**
+
 * Produce the `build/` directory
 
         $ git clone https://github.com/0x1eef/myip.wtf
         $ cd myip.wtf
         $ npm i
         $ npm run build:production
-        
+
 * Load the extension
     * Visit `chrome://extensions`.
     * Check `Developer mode` (top right hand corner).
@@ -27,6 +29,12 @@ to your browser.
     * Choose the `build/production/` directory from the file dialog.
     * Done.
 
+**Firefox**
+
+The [share/myip.wtf/xpi](share/myip.wtf/xpi) directory contains
+signed XPI files for Firefox users. After downloading an XPI file
+the extension can be added to the browser from `about:addons`.
+
 ## Sources
 
 * [GitHub](https://github.com/0x1eef/myip.wtf#readme)
diff --git a/package.json b/package.json
index 31a8a6f..0e94989 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,9 @@
 {
   "name": "myip.wtf",
   "version": "0.4.2",
+  "webExt": {
+    "sourceDir": "build/production"
+  },
   "dependencies": {
     "react": "^18.2.0",
     "react-dom": "^18.2.0"
diff --git a/src/manifest.json b/src/manifest.json
index 0483f73..7354e1f 100644
--- a/src/manifest.json
+++ b/src/manifest.json
@@ -14,5 +14,10 @@
     "256": "images/icons/wtf256x256.png"
   },
   "permissions": [],
-  "default_locale": "en"
+  "default_locale": "en",
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "{b9004e11-0d38-417e-8968-9adc2229a6c3}"
+    }
+  }
 }