feat: convert as web extension

works well in both firefox and chrome

package.json

@@ -22,11 +22,14 @@
         "*://musescore.com/*/*"
       ],
       "js": [
-        "dist/main.js"
+        "src/web-ext.js"
       ],
       "run_at": "document_start"
     }
   ],
+  "web_accessible_resources": [
+    "dist/main.js"
+  ],
   "dependencies": {
     "pdfkit": "git+https://github.com/Xmader/pdfkit.git",
     "svg-to-pdfkit": "^0.1.8",
@@ -48,6 +51,8 @@
   "scripts": {
     "build": "rollup -c",
     "watch": "npm run build -- --watch",
+    "start:ext": "web-ext run",
+    "start:ext-chrome": "npm run start:ext -- -t chromium",
     "bump-version:patch": "npm version patch --no-git-tag",
     "bump-version:minor": "npm version minor --no-git-tag"
   }

src/web-ext.js

@@ -0,0 +1,10 @@
+// entry file for the Web Extension
+/* eslint-disable no-undef */
+
+const MAIN_FILE = 'dist/main.js'
+
+const script = document.createElement('script')
+script.src = chrome.runtime.getURL(MAIN_FILE)
+script.addEventListener('load', () => script.remove())
+
+document.documentElement.appendChild(script)