Click on file > New Tab

you can add a new tab icon to your firefox navigation bar by clicking on view toobars customize that will open a box with a lot of icons you can drag onto your navigation toolbar, one is a new tab icon, just drag that onto your bar and click on it when you need a new tab.
or you can just right click on the tab bar itself and select new tab.

or any link you want to open in a new tab just right click on the link itself and choose open in new tab

Keyboard shortcut is Ctrl-T.

Thanks,
Cool I didn't know there were so many different ways to do this.
Sapphires