common/extensions/webextensions-selenium-example/manifest.json

{
  "manifest_version": 2,
  "name": "webextensions-selenium-example",
  "description": "Inject a div with id webextensions-selenium-example to verify that WebExtensions work in Firefox/Selenium" ,
  "version": "0.1",
  "content_scripts": [
    {
      "matches": ["https://*/*","http://*/*"],
      "js": ["inject.js"]
    }
  ],
  "applications": {
   "gecko": {
     "id": "webextensions-selenium-example@example.com"
   }
 }
}