You can disable memory cache, but I strongly recommend against it. It can severely impact your browsing. The only thing e-tags can do is link you between sites or exit nodes. They can't identify you (unless you're using your real identity over Tor on one of those sites, which is stupid). However, if you still want to do it, type about:config in the URL bar and click through the warning. type in: browser.cache.memory.enable and double click it so it says false.