Question about Internet Email Links to Entourage

I use Entourage exclusively for email instead of the Mac's Mail Program. For web browsing I use both Safari as well as Firefox. My question: Frequently I go to web sites which have a email link to click on to open up a email msg to email that specific person. The problem, whenever I do this it opens up the mail program, not Entourage and I can't figure out how to change this. I looked in both Firefox and Safari and see no options so I am thinking its something in OS X telling it where to default to. How can I go about doing this?