Export a file from cache?

I was trying to figure out how to “save as” a resource from cache without downloading it again.

A web has an <audio> tag, which fully-playable on my Firefox when I visit the page. But when I use “save audio as” context menu, Firefox tries to fetch the wav file again, but server doesn’t want to serve it for long and has already deleted it.

about:cache has a list of all files cached in memory and in disk

I followed the “in disk” part and opened the path in my system file browser. All files are there, and they are named in hex numbers. Don’t know which name is which file.

The about:cache page provides hex view of the content of file. I’m wondering why not add a “export/download” button?

Are there any way to “save as” a resource from cache only? Without re-downloading