When you key a search term into Google it often has a pretty good idea of what it is you are looking for. For example, if you key in “microsoft” it’s likely you are looking for the Microsoft.com page, and Google puts it up in the top search results position.

Google Speeds Up Firefox Searches

In cases like this, where Google assumes that it is very likely that you will click on the obvious choice for your search term, it now attempts to speed up the subsequent display of the the likely target page-that is, if you are using a Firefox (or other Mozilla-based) browser. What happens is that Google will anticipate your selection and “prefetch” the target page content while it’s waiting for you to click on its link. So, when you finally do request the page, it’s hopefully already in your cache, speeding up its display. If you click on another link instead, it will stop the prefetching process.

Why just for Firefox? Mozilla utilizes a function called “prefetching.” Here’s the definition of prefetching from the Mozilla Link Prefetching FAQ:

“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.”

It looks like another win for FireFox, which has now moved up from 39.7% of Google Tutor readers in March to 45% so far in April (versus Internet Explorer at 35.3%). If you have not yet downloaded Firefox, get it here. (You don’t need to dump IE; it will still be there.)

But wait, maybe you don’t think it’s a win for Firefox. In fact, depending upon how you feel about filling your cache and adding to your cookies, you might think the whole thing stinks. You see, if you don’t actually go to the presumed target web site Google prefetches, you’re still adding to the cache and potentially adding a cookie each time you perform a search. The extra pages in your cache can’t be a big deal, but you may or may not be thrilled about the cookies. Personally, it doesn’t really bother me as I visit so many web sites all day long, what’s a few more cookies and cached pages? But, that’s just me.

The good news is that if you don’t like the idea of prefetching, you can disable it. In Mozilla 1.3+, there is a preference in the UI to disable prefetching. See Preferences->Advanced->Cache to disable it. In Firefox, you can disable prefetching by doing the following:

1. Type “about:config” the address bar.
2. Scroll down to the setting “network.prefetch-next” and set the value to “False”.

With prefetching, you better hope that if while searching on your computer at work the first search result isn’t a porn site, and ends up getting downloaded into cache. If you have to explain that to an administrator who discovered porn in your cache, make sure to tell him or her that the content is flagged in a different way from content that is actually chosen to download. Explain that an x-moz: prefetch’ header is sent with the request, and the referrer header will match the Google search results page.

If you are techie, you might be interested in how this works. On searches where Google thinks it knows you’ll end up clicking the top search result, it inserts a special link tag, supported by Firefox and Mozilla, that tells the browser to download the top search result before the user clicks on the result. This tag is only inserted when it is likely that the user will click on the first link.

For example, when a Firefox user searches for “microsoft”, Google includes the following tag in the results HTML:

<link rel=”prefetch” href=”http://www.microsoft.com/”>

The official Mozilla Link Prefetching FAQ describes the behavior of this tag in detail.

If you are a webmaster, be aware that prefetching may impact your site by generating additional traffic usage, because the prefetch request will happen whether or not the user clicks on the result.

Mark Fleming is the founder of a new blog called Google Tutor & Advisor. Google Tutor & Advisor offers in-depth Tips, Techniques and Advice for Google Users.

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