Take a look at the menubar of your browser. You'll see some letters underlined, e.g. File Edit View ... (Press Alt if you don't see them.)
These are shortcuts. If you press Alt + F, the file menu will open, if you press Alt + E, the edit menu, Alt +V the view menu...
Every shortcut needs a unique letter, else there would be a conflict. If you have file and edit, which one should be opened when you press Alt + e?
The '&' marks the underlined letter and that's why it is always at a different position.