Have you ever been to a website with one browser, and then later with another only to realize that the contents displayed were different? Or have you been to a site without favorite browser only to read the note that your browser was not supported by it?
The websites in question are likely using techniques to detect the user agent, which contains information about the web browser and operating system used by the user.
A basic example is the Google search website. It detects the web browser to enable or disable the new Google Instant Search feature. Opera users for instance are not able to use the feature because Google uses browser sniffing to disable the feature for user's of that browser.
The Google Chrome extension is a basic extension which can detect if a page uses user agent detection. If it is enabled, it displays an icon in the Chrome address form, if not then nothing is displayed. Take a look at the screenshot below to see how it works.
User agent detection is not only used on sites to offer different contents to different browsers. Many advertising scripts are also using those techniques. That's why you for instance see the icon on ghacks as well, even though it is used by third parties and not by us.
The extension is probably nothing that users want to have installed all the time in the browser. It is however interesting to see which websites use user agent detection.
Evil Meter can be downloaded from the Chrome extensions gallery. This site is also an example of a site that detects the browser in a different way, considering that it displays an active install button if the page is accessed with the Google browser, and an inactive button if another browser is used.
Ghacks is a technology news blog that was founded in 2005 by Martin Brinkmann. It has since then become one of the most popular tech news sites on the Internet with five authors and regular contributions from freelance writers.