chore: add dev::firefox script

Author: Akryum

package.json

@@ -24,6 +24,7 @@
     "dev:vue3": "concurrently \"cd packages/shell-dev-vue3 && yarn dev\" \"cd packages/shell-host && yarn dev\"",
     "dev:chrome": "cd packages/shell-chrome && webpack --watch",
     "dev:chrome:prod": "cd packages/shell-chrome && cross-env NODE_ENV=production webpack --watch",
+    "dev:firefox": "cd packages/shell-firefox && webpack --watch",
     "dev:electron": "cd packages/shell-electron && npm run dev",
     "build": "lerna run build",
     "build:watch": "lerna run build --scope @vue-devtools/app-backend* --scope @vue-devtools/shared-* --scope @vue/devtools-api && lerna run build:watch --stream --no-sort --concurrency 99",
@@ -72,4 +73,4 @@
     "cypress": "=3.4.1",
     "webpack-dev-server": "^4.15.1"
   }
-}
+}