Hi,
I presume that you are talking about the Card Style and by firstname, lastname being shown presumably you mean the "title" of each contact card. You can change this to show the address as the title by changing your contacts view to show this instead of "File As" (which is the default). To do this:
1. Click on View.
2. Click on Arrange By.
3. Click on Current View.
4. Click on Customise Current View.
5. Click on Fields.
6. On the "Show Fields in this order" section, drag "E-Mail" to the top of the list.
7. Click on Ok.
8. Click on OK.
Now when you are looking at your contacts you should see that the title of each contact is now the e-mail address. This will look the same when you print out the contacts in Card Style (or any style associated with contacts).
Hope this helps.
J.