guzbug,
Hi, guz. Capgain's method works, but here's what I do. Go to the toolbar next to the URL address window and right click and choose "customize" from dropdown menu, then you can chose the cut, copy and paste icons and drag them each to the toolbar and in future they will be right there. To use them, highlight what you want to cut, or copy by pressing the left mouse button and holding it as you drag your cursor across the text and release when you have highlighted everything you want to copy or cut.
If neither method is working for you something is wrong and I'd recommend deleting firefox and reinstalling.
Newly