use parcel bundler for building

.gitignore

-node_modules/
+node_modules/
\ No newline at end of file
+.parcel-cache/
+dist/
\ No newline at end of file

.parcelrc

+{
+  "extends": "@parcel/config-webextension"
+}
\ No newline at end of file

package.json

 {
   "name": "firefox-url-shorter-extension",
   "version": "1.0.0",
-  "main": "index.js",
   "author": "Jonas Leder <jonas@jonasled.de>",
   "license": "MIT",
   "dependencies": {
+    "parcel": "^2.7.0",
     "web-ext": "^7.2.0"
   },
   "scripts": {
     "start": "web-ext run --verbose",
-    "build": "web-ext build"
+    "build": "parcel build src/manifest.json"
+  },
+  "devDependencies": {
+    "@parcel/config-webextension": "^2.7.0"
   }
 }