manifest.json

{
  "manifest_version": 2,
  "name": "Automatic imperial to metric convertion BETA",
  "version": "0.2.1",
  "description": "Automatically convert imperial units to metric units on all websites",
  "icons": {
     "48": "icon48.png",
    "128": "icon128.png"
  },
  "content_scripts": 
  [
    {
      "matches": ["*://*/*"],
      "js": ["content_script.js"],
      "run_at": "document_end"
    }
  ]
}