Open multiple websites with single click on toolbar icon.
There is other ways to achieve this functionality, most common is middle mouse click on bookmarks folder.
But some people don't have fast access to that folder, or don't have middle mouse click, etc...
On options page enter URL's that you like to be opened every time when toolbar icon is clicked.
For sorting them, you can delete particular entries with Del button, or edit already existing URL.
After you done customizing your list, don't forget to save it.
URL protocols (http://, https://...) are required.