Examine source code of MuteEmAll

{
  "manifest_version": 2,
  "name": "MuteEmAll",
  "version": "1.1.3resigned1",
  "description": "Automatically mute all Firefox tabs.",
  "icons": {
    "48": "./icon.png",
    "96": "./icon.png"
  },
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "mute-em.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{92c6b5b1-9c05-4de1-992a-b438b54d00b8}"
    }
  }
}