As the question says, where do each of the browsers store their offline data, be it cache, offline storage from html5, images, flash videos or anything web related that gets stored locally.
Firefox store the offline data in
~/.mozilla directory, to be more specific in
~/.cache/google-chrome directory for storing cache. Google chrome also uses
~/.config/google-chrome/Default directory for storing recent history, tabs and other things.
Like Chrome, Chromium uses as such with only the name changed. That is