Firefox can be configured to use various different types of proxies. To configure Firefox to use a SOCKS proxy, open the Firefox Preferences/Settings window. In Mac OS X, go to Firefox -> Preferences. In the Windows version of Firefox, go to Tools -> Options.

Go under the Advanced tab, and under the Network tab. From there, click on Settings.

Choose Manual proxy configuration. Leave everything empty except the SOCKS Host and Port. The SOCKS host and port should be the respective host and port.