Open all websites in a favourites sub folder

If you have a set of websites saved in a subfolder of your favourites, sometimes it can be helpful to open all the sites for comparison. Imagine you are house-hunting. You might have all your local estate agents in a folder named Estate Agents. If you point your mouse at this folder, you should see an arrow appear beside the folder. Click on this arrow open all of the websites in the folder, each in their own window.