If you want to see all URLs in the Firefox cache, there is a directory in your home directory ".mozilla/firefox". Inside that is a Cache directory with lots of files, some gzip compressed, some JPEGs, some in another format. So, if you want to see the contents of those files, You'd do something like this:
$ zcat .mozilla/firefox/etlltonne.default/Cache/FFC94D43d01
$ zcat .mozilla/firefox/etlltonne.default/Cache/00C94D43d01 | strings
$ file .mozilla/firefox/etlltonne.default/Cache/F0B4DEACd01
.mozilla/firefox/etlltonne.default/Cache/F0B4DEACd01 JPEG image data, JFIF standard 1.02
for the cache files that contain binary data.
If you want something more, you should install squid, enable one or more of the logs (for cache, access, MUA, and/or referer) and point your browser to the squid.