details

An object with the following properties:

tabId Optional

integer. Specify the tab to get the title from.

windowId Optional

integer. Specify the window to get the title from.

• If windowId and tabId are both supplied, the function fails and the promise it returns is rejected.
• If windowId and tabId are both omitted, the global title is returned.

A Promise that will be fulfilled with a string containing the browser action's title.

This code switches the title between "this" and "that" each time the user clicks the browser action:

function toggleTitle(title) {
  if (title === "this") {
    browser.action.setTitle({ title: "that" });
  } else {
    browser.action.setTitle({ title: "this" });
  }
}

browser.action.onClicked.addListener(() => {
  let gettingTitle = browser.action.getTitle({});
  gettingTitle.then(toggleTitle);
});