ACtl.TAB_ID
Constant that holds the ID of the tab the script is running in.
ACtl.TAB_ID Returns Type: number
A non-zero integer if the script is running in a tab.
Zero if the script is running in the background.
Example
Open a URL in the same tab the script is running in or in the #currentTab if the script is running in the background.
if( ACtl.TAB_ID ){
//If we are running in a tab
ACtl.openURL('http://example.com', ACtl.TAB_ID) ;
}else{
//If we are running in the background
ACtl.openURL('http://example.com', '#currentTab') ;
}