Can I modify cache file of browsers? Why is it so hard to find any resources about cache modification?

Question

this question is for study purpose, although I think it is a sensitive topic?

My question was really simple.

"How can I modify, instead of just extracting cache from Firefox?"

BUT as I did search on this topic exhaustively, more questions appeared.

First, from all resources I assume the verification of cache only happens in order to make sure local cache is identical to server's file, yet ** both the ETag and last-modification could be manipulated to cheat the server**. So my question 1 is,

why is firefox and other browsers striving to make sure nobody can modify cache, if not for forensics purpose?

Second, consulting this webpage, http://encase-forensic-blog.guidancesoftware.com/2015/02/firefox-cache2-storage-breakdown.html, why is cache considered "forensics?" I assume there is a way to prevent cache modification happening, but I can't find legitimate proof of that. So,

what is the method/mechanism that browsers like Firefox use to prevent cache modification, with such they are so confident that it can be even used as forensic evidence???

Ferromagnetic

Answer 1

Since no one answered (or perhaps wanted to answer) the question, I'll talk about what I found.

First of all, the older Firefox version did support cache modification. They used to store cache in the way "what you see is what you get"-- the original cache file, a .jpg, a .gif, or .flv.

However, due to some reason (as they said for improving functionality), they decided to change, and began to store cache in binary format with a "table" that contains last-modified date (it's kinda like "cache validation" which is to prevent cache modification by client, even though it looks like cache modification will only affect client side).

The way I managed to change cache so that website content looked differently on my end, is to go back to Firefox 28.0.

However there can be security concerns, yet since Firefox is open source software, you can also download original code and modify the browser, compile it by yourself.

Cache modification is rarely discussed yet it shouldn't be the reason why people can't find the answer.

Ferromagnetic