If you’re one of the many people who uses more than one browser (or if you’ve just downloaded and want to use that browser exclusively), you need to tell your operating system which one you’d like to use as your default.
If you love Firefox and support what it stands for, below are the steps to make it your browser of choice.
At the top of the Firefox window, click on the Firefox button (Tools menu in Windows XP) and then click Options (or on a Mac, in the Menu bar, select Preferences). Select the Advanced panel, click the General tab and then under the System Defaults section, click the “Check Now” button. When prompted, click “Yes” to set Firefox as the default. You can also read more on setting Firefox as your default browser.