If you are using certain versions of Firefox (e.g. 4, 7) you may find that the fly-out sub-menus don't work properly (they disappear as soon as you try to select them!).
To get round this program bug, either
1. Use another browser (e.g. Internet Explorer, Google Chrome); or
2. Hold down the left mouse button as you move the cursor over the fly-out sub-menu; when you get to the item you want, release the mouse button, then left-click as usual.