tabs.onActiveChanged

Fires when the selected tab in a window changes. Note that the tab's URL may not be set at the time this event fired, but you can listen to tabs.onUpdated events to be notified when a URL is set.

browser.tabs.onActiveChanged.addListener(listener)
browser.tabs.onActiveChanged.removeListener(listener)
browser.tabs.onActiveChanged.hasListener(listener)

Events have three functions:

addListener(callback)

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:

tabId

integer. The ID of the tab that has become active.

selectInfo

object.

windowId

integer. The ID of the window containing the selected tab.