Firefox Prefetching Something you may not realize is that Firefox has a setting that will prefetch websites and images to improve the user’s browsing experience, and it’s actually enabled by default. It will utilize your browser’s idle time to prefetch images and websites as determined by the webmasters.

Mozilla has an entire page setup to describe how the link prefetching mechanism works, and here is the summary that they provide:

Link prefetching is a browser mechanism, which utilizes browser idle time to download or prefetch documents that the user might visit in the near future. A web page provides a set of prefetching hints to the browser, and after the browser is finished loading the page, it begins silently prefetching specified documents and stores them in its cache. When the user visits one of the prefetched documents, it can be served up quickly out of the browser’s cache.

Webmasters can enable the prefetching by placing code like this in their website:

<link rel="prefetch" href="/images/big.jpeg">

The HREF is what points to the website or image that needs to be prefetched, and in this example a fullsize version of a thumbnail is cached so that it loads faster. This can obviously be a useful feature, but it can also result in unwanted cookies and cached items showing up on your computer. Even Google uses this to cache the first result that is displayed.

If you don’t want Firefox to do this then you’ll have to manually go and disable it:

  1. In the Firefox Address Bar type about:config and press Enter.
  2. Find the option that is named network.prefetch-next and double-click on it.
  3. Change the value to false.

I’m not quite sure how I feel about Mozilla prefetching content without the users ever knowing. To me that is something they should ask users whether they want to enabled it when initially setting up the browser, especially since it can store cookies for websites that you yourself never actually visit.

What do you think about the prefetching?

There Are 10 Comments

  1. First of all, great tip, thanks!

    I have a flat rate internet connection, so I don’t mind Firefox fetching stuff in the background, while I’m scrolling down the page.

    But: here in Denmark we have certain types of internet subscriptions, for instance you can choose to get billed by the megabyte (yeah, talk about medieval internet) and maybe prefetching could give these internet users’ bill where they actually pay for more than they’ve visited?

    // Lars

  2. Not only did I eliminate the prefetching in both Firefox & Thunderbird, but I also followed your Helpful Tip link and eliminated the System Beep in Windows! That has never made any sense to me and has driven me NUTS forever.
    Thanks! :D

  3. ñaaaa i have a megabyte…..from the medieval….hum….

    well i will still wait to telmex speed up the infinitum from 1 to 2 at least(méxico)

    hey another tip disable suport to ipv6 and redirection-limit to “10″ zero will speed up firefox

  4. I think the user should be made aware of prefetching…As of now that’s not the case…hopefully that changes someday.

  5. Lars K Jensen wrote:
    But: here in Denmark we have certain types of internet subscriptions, for instance you can choose to get billed by the megabyte (yeah, talk about medieval internet) and maybe prefetching could give these internet users’ bill where they actually pay for more than they’ve visited?

    That’s a really good point, and something that I didn’t think about. Anyone that is getting charged according to the amount of bandwidth they use would definitely not like a feature like this.

    Grateful wrote:
    Not only did I eliminate the prefetching in both Firefox & Thunderbird, but I also followed your Helpful Tip link and eliminated the System Beep in Windows! That has never made any sense to me and has driven me NUTS forever.
    Thanks! :D

    That’s what we’re here for! We really appreciate you taking the time to let us know that we helped you. :) It makes us feel all warm and fuzzy inside.

  6. From the same Related Posts I followed the Reducing Your Memory Usage In Firefox link and added the config.trim_on_minimize … True setting to both Firefox & Thunderbird.
    You give very easy to follow directions and it WAS “quick and painless” as advertised! ;)

  7. Grateful wrote:
    You give very easy to follow directions and it WAS “quick and painless” as advertised! ;)

    We’re all about trying to make things as painless as possible, and I’m just glad that our other tips have been working out for you. :D

  8. I think the very idea of prefetching data that may not be accessed is another contribution to both bandwidth saturation and absurdity : why download more than required? To save a few milliseconds?

    Moreover, not sure how cached data is handled by anti-advertisement code/software; as far as I know cached data is considered good (with Ad-Muncher software, anyhow, I think).

    Also, as mentioned, “unrequested” cookies has of course privacy concerns.

    Finally, I never noticed any great speed enhancement with “network.prefetch-next” set to true.

    Need I say I’ve disabled Firefox prefetching? ;)

  9. Ryan,

    It seems to have put a little more speed to page rendering.
    Wonder how someone could have disabled it on Thunderbird?
    :?

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