None.

A Promise that will be fulfilled with an object which has the following properties:

name

string value representing the browser name, for example "Firefox".

vendor

string value representing the browser's vendor, for example "Mozilla".

version

string representing the browser's version, for example "51.0" or "51.0a2".

buildID

string representing the specific build of the browser, for example "20161018004015".

Get and log the browser's name:

function gotBrowserInfo(info) {
  console.log(info.name);
}

let gettingInfo = browser.runtime.getBrowserInfo();
gettingInfo.then(gotBrowserInfo);