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.   
Connection Settings Dialog  Direct connection to the Internet
     
    This is the default optionpreference. Choose this if you don't want  to use a proxy. Auto-detect proxy settings for this network  Choose this if you want Firefox to automatically detect the proxy settings for your network.   Manual proxy configuration
     
Choose this if you don't have a proxy location (URL). Ask your system administrator for the names and port numbers of the servers
running proxy software for each network service and enter the information in the appropriate fields. Automatic proxy configuration URL
 
If your workplace has a proxy configuration file, ask the system administrator for its URL and enter it here. Click Reload to load the settings. Cache  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.

Use up to ... MB of space for the cache  Allows you to specify the maximum size, in megabytes, of the cache on your computer.
 Clear Now  Immediately clears the current contents of the cache, freeing the disk    space used by the cache. Update tab Firefox can check whether updates to installed add-ons or to   Firefox itself are available. Automatically check for updates to: By default Firefox automatically checks for updates to itself, to add-ons, and to search engines so you'll always know you have the most up-to-date version. You can change this behavior by changing the appropriate checkboxes here.