Open a new tab in FireFox

If you click on a hyperlink with your mouse's scroll-wheel (as if it were a button), it will open in a new tab in the background.

You can also hold down Ctrl and click on the hyperlink to do the same.

This is really handy if you are reading an article with numerous links within. You just click on each of them as you go down, and then - when you are finished with the article - the pages will have finished loading in the background for you.