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:
- In the Firefox Address Bar type about:config and press Enter.
- Find the option that is named network.prefetch-next and double-click on it.
- 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?