User e-mail addresses on Facebook have come a long way. For years, Facebook converted them into a static image to keep potential spammers and data thieves at bay. As a result, it made copying them a serious pain, as you'd need to have whatever e-mail tool you were using in one window, and that user's profile in another.
Earlier this month, Facebook changed it to plain text, which lets you copy and paste the address instead.
If you're too lazy to do that, or just find yourself doing it several times a week, you could save yourself some trouble by installing Facebook E-mail Links, a new Firefox extension that automatically converts these links into a mailto: URL. That means the next time you click on someone's e-mail address, it'll open up in whatever local or Web-based e-mail tool you use.
This is one of those great examples of a one-trick extension that you can install and forget about. And in case you're confused about how to tweak Firefox to use something other than Outlook (or whatever else the default e-mail client is on your computer), you can follow, which still works.