where is firefox's cache folder, the one with the images ?

i looked but can't find it. i went to the about:cache and it is full of empty folders and the first files i do see all say

_cache_001
_cache_002
_cache_003
_cache_map_

and are not readable. i just want to snip whatever images that my webpages display, if i can identify them as images first.

thank you.