If you don't have a default browser set already, then Android will prompt you to set one when you open a link from another application.

If you do have a default browser set (or if you're not sure), then open Android's "Settings" app, choose "Applications: Manage Applications: All." Then tap on your current default browser (probably the built-in Browser app), and press the "Clear defaults" button.

Thank you. Android did not prompt me to set a default browser (at least I don't remember that). When I go to Settings, there is "Applications: Manage Applications" but not "Applications: Manage Applications: All." Firefox is on the list of applications. On the home screen there is an icon (apparently the earth with a green ring around it but I cannot tell what the default browser is.

After choosing Manage Applications, there should be four tabs across the top of the screen, which let you view different sets of apps like "Third party" (or "Downloads"), "Running," and "All." To manage the built-in Browser app, you will need to switch to the "All" tab on the Manage Applications screen.

I've done this and when I get to the Google Search tab and click on it the bottom says No Defaults Set, so I can't clear them. Please help

DrewMeister, instead of choosing Google Search from the list of apps, choose "Browser" (or whatever the name of your current default browser is).