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