tabs.captureVisibleTab()

Creates a data URI encoding the image of an area of the currently active tab in the specified window. You must have the <all_urls> permission to use this method. (Alternately, Chrome allows use of this method with the activeTab permission and a qualifying user gesture).

This is an asynchronous function that returns a Promise.

var capturing = browser.tabs.captureVisibleTab(
  windowId,               // optional integer
  options                 // optional extensionTypes.ImageDetails
)

windowIdOptional

integer. The target window. Defaults to the current window.

optionsOptional

extensionTypes.ImageDetails.

A Promise that will be fulfilled with a data URL which encodes the captured image. May be assigned to the 'src' property of an HTML Image element for display. If any error occurs the promise will be rejected with an error message.

Capture an image of the active tab in the current window, with default settings:

function onCaptured(imageUri) {
  console.log(imageUri);
}

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

browser.browserAction.onClicked.addListener(function() {
  var capturing = browser.tabs.captureVisibleTab();
  capturing.then(onCaptured, onError);
});