The Windows Set Default Programs utility has the option to set Firefox 36 as your default browser. Instead of browsing to the utility through the Windows Control Panel, you can access it from Firefox's Options window. Set Firefox to open all browser file types by default or choose the file types you want the browser to open through the Set Program Associations window.
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Click the Firefox Open Menu button, resembling three lines, and choose Options from the drop-down menu to open the Options window.
Click the General tab and then select the Always Check if Firefox is Your Default Browser check box in the Startup section to ensure that Firefox checks its default status every time you launch the browser. Click the Make Default button in the Startup section to open the Windows Set Default Programs window. Clicking the Make Default button automatically launches the Windows Set Default Programs utility without your having to manually navigate to the utility through the Windows Control Panel.
Choose Firefox from the Programs box and select Set This Program as Default to set Firefox as the default program to open all standard Web browser protocols and file types. Click the OK Button to save the setting.
Select Choose Defaults for This Program to open the Set Program Associations window, which displays the standard Web browser protocols and file types that you can open with Firefox.
Select the check box next to each browser file type and protocol that you want Firefox to open by default. For example, if you want Firefox to open HTML files on your computer, select the HTML check box. Although Firefox can open file types that Windows does not associate with the Internet or Web browsers -- such PDF, MPG and JPEG files -- only browser file types and protocols that the operating system has determined Firefox can handle are listed on the Set Program Associations window.
Click the Select All check box to simultaneously select all. Note that all the check boxes in the Set Program Associations window are automatically selected and cannot be changed if you already set Firefox as your default browser. Click the Save button to set the associations for Firefox and reopen the Set Default Programs window.
Click the OK Button after the Set Default Programs window reopens and then click "X" in the upper right corner to close the window.
Click the OK button on the Options dialog window to close the window. Although you can automatically launch the Set Default Programs utility window from the Firefox Options dialog window, closing the Set Default Programs window does not automatically close the Options dialog window. After you set Firefox as your new default browser, Firefox is Currently Your Default Browser displays in the Startup section of the Options window.