manifest.json

{
    "manifest_version": 2,
    "name": "kittenbook",
    "description": "Replace all the pictures on facebook with pictures of kittens or puppies",
    "version": "0.0.1",
    "content_scripts": [
        {
            "matches": ["*://www.facebook.com/*", "*://www.pinterest.com/*"],
            "js": ["main.js"]
        }
    ]
}