Completely disable Firefox disk caching (etc)

http://nctritech.wordpress.com/2012/12/08/completely-disable-firefox-disk-caching-for-speed-and-paranoia/

1. Open Firefox. Go to the address bar, type about:config and hit [Enter].
2. It might warn you not to play around. Click “I’ll be careful, I promise!”
3. Type “prefetch” into the search box. You should see an option called “network.prefetch-next” which you can double-click to change to “false.”
4. Search for “cache.disk” this time. Change “browser.cache.disk.enable” to “false” and change “browser.cache.disk.capacity” to “0.”
5. Close and re-open Firefox.
6. Hit [Ctrl] + [Shift] + [Delete] to bring up the “Clear Recent History” box. Change your time range to “Everything” and make sure “Cache” is checked. This erases the entire disk cache.
7. For the really paranoid, install CCleaner (don’t install anything else it offers to install while you do it), find the “Wipe Free Space” option at the bottom of the left column, right-click on it, and choose “clean.” (It might warn you that it’s going to delete stuff, but proceed anyway.) This erases the contents of all of the empty space on the hard drive, including anything that was in the disk cache you just deleted and anything that has ever been deleted from the computer.
8. [Update for newer Firefox versions] Firefox stores thumbnails of pages you visit for the new “New Tab” page previews. To get rid of this while you’re in about:config, right-click somewhere and go to New -> Boolean, call it browser.pagethumbnails.capturing_disabled and set it to true. Restart Firefox and no more behind-your-back thumbnails.