This article explains the settings available in the Advanced panel of the Firefox OptionsPreferences page. These are settings that aren't used very often, such as proxy settings and various other advanced settings that only some people need.
Your organization or Internet service provider may offer or require you to use a proxy. A proxy acts as an intermediary between your computer and the Internet. It intercepts all requests to the Internet to see if it can fulfill the request using its cache. Proxies are used to improve performance, filter requests, and hide your computer from the Internet to improve security. Proxies are often part of corporate firewalls.
Pages you view are normally stored in a special cache folder for quicker viewing the next time you visit the same page. You can specify the amount of disk space the cache can use here. You can also immediately clear the contents of the cache.
Certificates help perform encryption and decryption of connections to websites.