For site designers it's really difficult as there's so much "stuff" on a site this size, that if you don't cache as much as possible, the site takes forever to load up when you visit it. This is especially problematic when you're dealing with tons of pictures, where a single pic can be megabyte sized! Normally the cache is for stuff that never or rarely changes... It's the same every visit, so caching it helps the site load quicker as it's saved on your computer and doesn't need to download to your screen.
If you've never cleared your cache before, in Firefox, up top, click on "Tools" then select "Options", the window should open in a new tab for you. On that page, select "Advanced" from the left side menu. The third item down is "Cached Web Content". Off to the right side you have the option to "Clear Now". Before you click it, look to see how much cache is presently being stored, then click it and you should see it go to zero. If you have a lot of cache stored, you also have the option to increase the storage size.
If you've never cleared your cache before, in Firefox, up top, click on "Tools" then select "Options", the window should open in a new tab for you. On that page, select "Advanced" from the left side menu. The third item down is "Cached Web Content". Off to the right side you have the option to "Clear Now". Before you click it, look to see how much cache is presently being stored, then click it and you should see it go to zero. If you have a lot of cache stored, you also have the option to increase the storage size.