browser.action.onClicked.addListener(listener)
browser.action.onClicked.removeListener(listener)
browser.action.onClicked.hasListener(listener)

Events have three functions:

addListener(listener)

Adds a listener to this event.

removeListener(listener)

Stop listening to this event. The listener argument is the listener to remove.

hasListener(listener)

Check whether listener is registered for this event. Returns true if it is listening, false otherwise.

callback

Function that will be called when this event occurs. The function will be passed the following arguments:

tab

tabs.Tab. The tab that was active when the icon was clicked.

OnClickData

An object containing information about the click.

modifiers

An array. The keyboard modifiers active at the time of the click, being one or more of Shift, Alt, Command, Ctrl, or MacCtrl.

button

An integer. Indicates the button used to click the page action icon: 0 for a left-click or a click not associated with a mouse, such as one from the keyboard and 1 for a middle button or wheel click. Note that the right-click is not supported because Firefox consumes that click to display the context menu before this event is triggered.

When the user clicks the icon, disable it for the active tab, and log the tab's URL:

browser.action.onClicked.addListener((tab) => {
  // disable the active tab
  browser.action.disable(tab.id);
  // requires the "tabs" or "activeTab" permission, or host permissions for the URL
  console.log(tab.url);
});