Tip: if you don't get that message, go to your AOL inbox and click "Options" (top right). Select "Settings", and choose "Compose" (left, on the next page). Scroll all the way down, and click "Use AOL Mail as your email client when browsing web pages" - now read on!
Tip: change this options any time by going to "Firefox > Options > Options". Select the "Applications" tab, and type "mailto" in the text box, and pick an option from the dropdown: To delete it from the list, choose "Application Details", select "AOL Mail", click "Remove" and then "OK". (The best is to choose another email program and select to "Remember" it.)
Tip # 2: know that if you keep "Always ask" as the default, you can just double-click on the email program you want to use, whenever you clicked on an email link!