How to save all binary web browser traffic

Question

I'm using Firebug and NetExport on Linux to save all web browser communication (mostly HTTP and HTTPS requests and responses). However, in my .har file I see messages like this:

The resource from this URL is not text: http://...

Instead of these messages I want to see the actual, full binary content (not even a single bit transformed or changed or lost). How do I get that?

I have root access on the local machine. A solution using Chrome or Firefox is fine.

Please don't recommend that I download binary files manually, there are too many of them, and I need to time the downloads perfectly, with the correct set of cookies (which may expire by the time I download manually). Please don't recommend non-Linux solutions, I have access only to Linux systems. Please don't recommend Wireshark (or tcpdump), because it can't save decrypted HTTPS traffic if I don't have the private key of the server.

Answer 1

In about:config I've set extensions.firebug.cache.mimeTypes to a space-separated list of MIME types, restarted Firefox, and everything got saved.

application/x-shockwave-flash image/gif image/jpeg image/png application/octet-stream

Please note that some documents are still missing from the .har file, I get this:

Reload the page to get source for: http://...