If you have multiple browser installed, when you want to make one a default browser, the easiest way to explain it is, email yourself a link, then open the email with your email app on your phone, once opened, simply click on the link and it will show all the browsers you have installed, then add a check mark to use by default, then choose the browser you want, then that should be your default browser, there is another way to do so also, go into settings/applications/manage applications/All, then scroll to the stock browser and check to see if that is marked as the default browser, if it is, then clear the default browser, then when you open another link it will show you your browsers and again choose which one you want to make default.
