Resources > Engines
This page lists the common browser engines:
Introduction
A browser engine — also called a layout engine or rendering engine — is the core of a web browser, responsible for rendering web pages.
A browser engine can be used by many different browsers. For example, the Gecko engine is used by Camino, Epiphany, Fennec, Firefox, Galeon, K-Meleon, Mozilla, Netscape 6-9, SeaMonkey, and others. Browsers which use the same version of the same engine should display pages the same if the browsers are configured the same, but there can be differences. For example, Chrome and Safari use the same browser engine, but they have different JavaScript interpreters, which can create rendering differences. Or, for example, some browsers have different default styles — e.g. default background colours — which can also create rendering differences.
Common Browser Engines
There are four major browser engines in use today, not counting those used for mobile devices:
- Gecko : developed by the Mozilla organization, this is a free, open source engine used by many browsers, of which the best known are Firefox, SeaMonkey, and Netscape 6-9.
- Presto : developed by Opera Software, this is a proprietary engine used in recent versions of the Opera browser.
- Trident : developed by Microsoft, this is a proprietary engine used by many browsers, of which the best known are Internet Explorer and most AOL browsers for Windows.
- WebKit (or AppleWebKit): developed by Apple, this is a free, open source engine based on the KHTML engine, used by a small number of browsers, including Chrome, Safari, and OmniWeb.
Minor browser engines include:
- iCab : developed for versions 1-3 of the iCab browser, which runs under OS X. (Later versions of iCab use the Apple WebKit.)
- KHTML : developed for the Linux KDE Desktop, is used in the KDE Konqueror browser, and more importantly was used to create Apple’s WebKit engine; the WebKit engine can legitimately be called a KHTML engine.
- Tasman : developed by Microsoft for its extinct Apple browsers.
The most common browser engines, and their versions, are:
Note : the numbering of Internet Explorer’s browser engine became really strange after IE7: IE8 uses Trident 4, but IE6 uses Trident IV; and IE9 uses Trident 5, but IE7 uses Trident V. Presumably no one at Microsoft knows that IV is 4, or V is 5: the engine for IE8 should have been called Trident VI or Trident 6; and the engine for IE9 should have been called Trident VII or Trident 7.
Identifying Browser Engines
There are a few principles a designer should consider when trying to identify browser engines:
Identifying the engine should rarely be necessary: if you design to the standards, pages should work well without browser-specific code. Exception : old versions of IE often require some IE-specific code.
Identifying the version of the engine should even more rarely be necessary: if you design pages to gracefully degrade with older browsers — i.e. to work with older browsers, though perhaps less lovely — pages should work well without version-specific code. Exception : old versions of IE often require some version-specific code.
It is better to identify the browser engine than it is to identify the browser: it is the browser engine that does the rendering, and several browsers may use the same browser engine.
It is better to use Internet Explorer Conditional Comments to reveal IE-specific code, because conditional comments are absolutely reliable: they work even if JavaScript is disabled, and they can’t be tricked by browser spoofing.
It is better, when a JavaScript-based browser sniffer must be used, to use a proven, standard module to identify the engine. The module should use Internet Explorer Conditional Comments to identify IE, and should analyze the lowercase equivalent of
navigator.userAgentto identify other browsers.It is critical to examine the userAgent string carefully to minimize the risk of being fooled by browser spoofing. For example, since “gecko” appears in the Safari userAgent string, but Safari is not a Gecko browser, it is wrong to assume that “gecko” indicates a Gecko browser.
This author has observed the following aspects of the lowercase equivalent of the userAgent string; this information is useful in creating an effective browser sniffer:
- KHTML-based browsers — e.g. Chrome, Konqueror, Safari — have “khtml”.
- WebKit-based browsers — e.g. Chrome and Safari — have “gecko”, “khtml”, and “safari”.
- Chrome has “chrome/” (note the slash), “gecko”, “khtml”, and “safari”.
- Opera has “opera” and may contain “gecko” or “msie”.
- Gecko-based browsers have “gecko/” (note the slash).
- MSN-TV has “msie” and “web-tv”.
- IE has “msie”.
- IE 8 usually has “trident/4”.
- IE 9 has “trident/5”.
A sample browser sniffer exists which applies the above principles.