Apple introduced the Safari browser in January of 2003. Since then, it's matured to include extensions, an RSS reader and even a Windows counterpart. Still, many users prefer another browser. Since Safari is set as the default on every new Mac, you'll have to make the switch manually. Otherwise, Safari will launch whenever a browser is called for (clicking a link in an email message, for example), instead of your preferred browser. Here's how to change that.
First, launch Safari. From the Preferences menu, select General. At the top of the screen you'll see a drop-down labeled "Default Web Browser." Click it, hit Select and then navigate to your choice. That's it. From that point on, your Mac will use your selection as the default.
If you're in the habit of switching back and forth between default browsers (for example, to test your website for different users), the $12 Choosy utility may give you the flexibility you need.