Completely disable Firefox disk caching and thumbnail generation for speed and paranoia

A comment on an article on Ars Technica reminded me that people have been convicted of possession of child pornography in the past based solely on the contents of their web browser’s cache (Internet Explorer calls them “temporary internet files.”) The problem with this is that these days, you don’t necessarily have to see or click on anything to have it load into your browser cache. Ignoring questionable ads and unexpected pop-ups and someone else touching your computer as a source of such garbage, actual “features” like link prefetching can do this by loading the contents of certain links on a page in anticipation of you clicking through them while never necessarily doing so. It’s pretty scary to think about such things, but they can and do happen, and if some forensic guy ever sees the contents of your hard drive, you don’t want to have to worry about some prefetched stuff you didn’t know was there landing you in hot water, especially in the “guilty until proven innocent” manner criminal court juries tend to operate.

Torrents, private emails, and other things that aren’t necessarily illegal at all (yet definitely deserve to be kept private) are stored in your browser cache, too. Even if you’re not concerned about the remnants of the virus you just got quarantined having opened questionable websites for you, you might not want copies of your email to your boss with whom you’re having an affair being found by your nosy significant other, or you might have caught your kids downloading something they shouldn’t have using BitTorrent and want to make sure records of their faux pas isn’t floating about in the browser cache for the next few months.

Then there’s the technical aspect: more files on disk is generally a bad thing, because a folder with 5,000 entries is far slower to search through for one file than a folder with 100 entries (or no folders at all). Wouldn’t it be awesome to alleviate both the paranoid legal risk as well as speed up your browser and prevent it from polluting your hard drive with thousands of files you don’t care about? If you use Mozilla Firefox, it’s actually somewhat simple to turn off prefetching and disk caching once you know how. Note that memory caching is still in place, so you do still have the speed benefits of caching; note also that memory caching can still end up in your paging file, so this isn’t a 100% foolproof thing, but in terms of eliminating risk it’s a huge leap forward.

  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.

While you’re at it, you might want to install NoScript and Adblock Plus, and learn how to use them to protect against these things landing on your browser in the first place, but that’s beyond the scope of this post. Happy faster browsing, and tell your boss in your next email that I’ll see her this weekend. 😉 xoxo

9 thoughts on “Completely disable Firefox disk caching and thumbnail generation for speed and paranoia

  1. Dayum, but you’re a great teacher. I have been on fifty freakin’ pages trying to do this – and all except yours were garbled crap assuming the reader was an IT genius or something. It would be a great world if more were like you in explaining otherwise mystical crap. Kudos. I needed this done because I never use IE anymore owing to Windows 7 not allowing the home edition user access to group policy. I know why they do this, and it’s precisely what you mentioned – to keep that thumbnail file intact for forensic audits and hanging people who have never even been to a soft porn site.
    What I did with the thumbnail cache on IE was to use Recuva and delete every single “deleteable file. I hope that’s enough. Wish I could blast that one, too.
    Thanks ever so much for your help

    1. Thank you for your kind words and I’m glad to have been helpful. If you use Windows, you may want to consider turning on the option in the registry that wipes the paging file data on shutdown. It is accessible in Group Policy but the registry option can be easily found and changed too. I believe it’s under HKLMCurrentControlSetControlSession Manager. Possibly under a key called Memory Management. I haven’t looked in some time but it’s somewhere in that area.

  2. NCT there’s a You tube thingee which deals with disabling the Wintows thumbnails folder in the Windows 7 home edition through the registry editor. It’s: .

    Looks like it’s easy to follow if you’re careful and attentive, and I will disable that as well. Windows has absolutely no right to do this without making it perfectly clear to the buyer what they are doing with their private photos and videos – especially without making it easy to disable by your normal user. Gawd these people piss me off. The vast majority of normal home computer users using an IE browser haven’t a clue what’s being done with THEIR private information. It’s the very same thing as if, before computers, the Post Office was keeping copies of all your personal letters and photos without telling you, or allowing you to opt out. I should make it clear that I have absolutely nothing to hide, but that fact alone does not mean didley squat in the world we now live in. Google, Microsoft – they’re all in bed with Uncle Sam and know where their bread is buttered.

    1. I run Linux on nearly everything I own now, with full disk encryption for home folders, external hard drives, and I even wrote a shell script that sets up user-specified folders and files such as Firefox caches or Flash cookies in a RAM disk of sorts (tmpfs) that is lost at power off and rebuilt empty at each boot. The only place I still need Windows is my big media processing hardware for running Adobe CS6 software. If you are interested, I’ve installed Linux Mint on a few machines for other people and found it to be both stable and usable. The only disadvantage is it’s based on Ubuntu (which I do not like at all.)

      1. Just to clarify, you have it the wrong way round, ubuntu is based on Linux, well, Debian to be more precise, which is based on Linux.

  3. Wow, just what I was looking for, thanks so much. However, the CCleaner wouldn’t wipe the drive’s Free Space by either method, just keeps going and going and going. Seems like Windows 8.1 is a tough cookie to crack. Any suggestions?

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