I want to know the functions of Firefox in browsers

Please see:-

Firefox web browser | Faster, more secure, & customizable
The Firefox Web Browser is the faster, more secure, and fully customizable way to surf the web.

Firefox web browser | Faster, more secure, & customizable (http://www.mozilla.com/firefox/)

Firefox web browser | Faster, more secure, & customizable (http://www.mozilla.com/firefox/)
Mozilla | Firefox web browser & Thunderbird email client Mozilla is a global community dedicated to building free, open source products like the award winning Firefox web browser and Thunderbird email software.
Mozilla | Firefox web browser & Thunderbird email client (http://www.mozilla.com/)