function onRemoved(cookie) {
  console.log(`Removed: ${cookie}`);
}

function onError(error) {
  console.log(`Error removing cookie: ${error}`);
}

function removeCookie() {
  var removing = browser.cookies.remove({
    url: "example.com"
  });
  removing.then(onRemoved, onError);
}

browser.browserAction.onClicked.addListener(removeCookie);

{

 "description": "RemoveCookie",
 "manifest_version": 2,
 "name": "remove-cookies",
 "version": "1.0",
 "icons": {
 "48": "icons/icon.png"
 },

"background": {
 "scripts": ["background.js"]
},

"browser_action": {
  "default_icon": "icons/icon.png",
  "default_title": "Remove Cookie!"
},

"permissions": [
 "*://*.example.com/*",
 "cookies"
]
}