You can find the location of the cache on the about:cache page (open that page via the location bar like a website). Only large image and media files are stored as individual files on disk.
Other files are stored in a few large container files (_CACHE_XXX_) in the cache folder and not as separate files on disk.
The individual files on disk have random names without a file extension for security reasons: you can't open an application or start a downloaded virus inadvertently by clicking a file in the cache folder.

You can look at this extension for easier access to files in the cache.

• Cache Viewer: https://addons.mozilla.org/firefox/addon/2489

In Firefox it is called the cache. to find the location of the cache type about:cache into the location bar. As a security measure, files in the cache are given random file names.

The CacheViewer add-on may be of use to you.