Navigators do not interpret HTML, javascript or CSS and don't display images, animations and transparency the same way.

When you can enable java (JRE 6.0), install the "plugins" (Flash, Ipix, Quicktime, Acrobat Reader...), positions on the screen may change.

As they find a lot of compatibility problems, webmasters may redirect the pages according to the detected navigator or create several style sheets or write for the most famous navigators or the most frequent or their favourite. Here is the danger when you use these add-ons pretending anonymous browsing as they may block your referrer -"HTTP_REFERER"- or refuse cookies (several routines as the style switcher won't work) or they may mask your browser identity (if you use them, the menu on the left may overlap the text, may be without the CSS popup and some text may not appear in many pages).

This page has been generated for your navigator identified as:
CCBot/2.0 (
This page won't give the same results with another identifier.

Consequences on mirrors

As the source code may depend on the User Agent, the best is to identify the browser at the time of a capture.
It may also be a way to complete a mirror as identified robots are sometimes stopped by some sites or providers ( for example).

HTTrack gives you the choice between 30 identifiers according to the browser and the operating system and an option to send any User Agent string.

Before offline browsers filtering by, you could mirror this site with different browser identities (a recent and an old browser for example) and get very different pages. With Mozilla (+ Multizilla), Firefox (+ User Agent Switcher), Konqueror, K-Meleon or by connecting to wannabrowser, you will get very different sources: with or without javascript, with alternate stylesheets or not...
In the site, the page redirects any MSIE 6 compatible to the home page and displays the code to other browsers. The same can be done for robots or for a masked identifier.

When you update your navigator, update the capture if it is still possible.

A few compatibility problems

Problems with this site:

All the tests led to modifications (and new bugs!).

The validation of your source code at the W3C can help you to find errors and tidy your code.
Problem are often linked to javascript or CSS.


PHP allowed me to remove most of the javascript routines.


The validation of your CSS styles at the W3C can help you to find errors and tidy your code.
PHP allowed me to detect the browser and send adapted styles (not recommended).
The page about CSS lists the solutions for the site.
Also online, you can find an introduction to page debugging.
You will also find a few pages describing a way of building a tableless stylesheet which will be compatible with many browsers.

A list of existing browsers can be found at Dan's Web Tips.
You can have a look at the comparison of web browsers from Wikipedia.
Web browser standards support are detailed at

Browser statistics here.

For your captures, don't forget to test and compare.

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With javascript