A web browser (commonly referred to as a browser) is a software application for retrieving, presenting and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier (URI/URL) that may be a web page, image, video or other piece of content. Hyperlinks present in resources enable users easily to navigate their to related resources.
Marc Andreessen with the release of Mosaic, "the world's first popular browser", which made the World Wide Web system easy to use and more accessible to the average person. Andreesen's browser sparked the internet boom of the 1990s. The introduction of Mosaic in 1993 – one of the first graphical web browsers – led to an explosion in web use. Andreessen, the leader of the Mosaic team at National Center for Supercomputing Applications (NCSA), soon started his own company, named Netscape, and released the Mosaic-influenced Netscape Navigator in 1994, which quickly became the world's most popular browser, accounting for 90% of all web use at its peak (see usage share of web browsers).
Microsoft responded with its Internet Explorer in 1995, also heavily influenced by Mosaic, initiating the industry's first browser war. Bundled with Windows, Internet Explorer gained dominance in the web browser market; Internet Explorer usage share peaked at over 95% by 2002.
Opera debuted in 1996; it has never achieved widespread use, having less than 2% browser usage share as of February 2012 according to Net Applications. Its Opera Mini version has an additive share, in April 2011 amounting to 1.1% of overall browser use, but focused on the fast-growing mobile phone web browser market, being preinstalled on over 40 million phones. It is also available on several other , including Nintendo's Wii video game console.
In 1998, Netscape launched what was to become the Mozilla Foundation in an attempt to produce a competitive browser using the open source software model. That browser would eventually evolve into Firefox, which developed a respectable following while still in the beta stage of development; shortly after the release of Firefox 1.0 in late 2004, Firefox (all versions) accounted for 7% of browser use. As of August 2011, Firefox has a 28% usage share.
The most recent major entrant to the browser market is Google Chrome, first released in September 2008. Chrome's take-up has increased significantly year by year, by doubling its usage share from 8% to 16% by August 2011. This increase seems largely to be at the expense of Internet Explorer, whose share has tended to decrease from month to month. In December 2011, Chrome overtook Internet Explorer 8 as the most widely used web browser but still had lower usage than all versions of Internet Explorer combined. Chrome's user-base continued to grow and in May 2012, Chrome's usage passed the usage of all versions of Internet Explorer combined. By April 2014, Chrome's usage had hit 45%.
Internet Explorer was deprecated in Windows 10, with Microsoft Edge replacing it as the default web browser.
In addition to being freeware, Netscape Navigator and Opera were also sold commercially.
Internet Explorer, on the other hand, was bundled free with the Windows operating system (and was also downloadable free), and therefore it was funded partly by the sales of Windows to computer manufacturers and direct to users. Internet Explorer also used to be available for the Mac. It is likely that releasing IE for the Mac was part of Microsoft's overall strategy to fight threats to its quasi-monopoly platform dominance – threats such as web standards and Java – by making some web developers, or at least their managers, assume that there was "no need" to develop for anything other than Internet Explorer. In this respect, IE may have contributed to Windows and Microsoft applications sales in another way, through "lock-in" to Microsoft's browser.
In January 2009, the European Commission announced it would investigate the bundling of Internet Explorer with Windows operating systems from Microsoft, saying "Microsoft's tying of Internet Explorer to the Windows operating system harms competition between web browsers, undermines product innovation and ultimately reduces consumer choice." Microsoft Corp v Commission
Safari and Mobile Safari were likewise always included with macOS and iOS respectively, so, similarly, they were originally funded by sales of Apple computers and mobile devices, and formed part of the overall Apple experience to customers.
Some commercial web browsers are paid by search engine companies to make their engine default, or to include them as another option. For example, Yahoo! pays Mozilla, the maker of Firefox, to make Yahoo! Search the default search engine in Firefox. Mozilla makes enough money from this deal that it does not need to charge users for Firefox. By virtue of common ownership, Microsoft Edge, Internet Explorer, and Google Chrome default to their respective vendors' own search engines, Bing and Google Search, and may integrate with other platforms offered by the vendor. This encourages the use of their first-party services, which in turn, exposes users to advertising that can be used as a source of revenue.
]] [[File:Browser Market Map June 2015.svg|thumb|Most used web browser by country, as of June 2015.
]] The primary purpose of a web browser is to bring information resources to the user ("retrieval" or "fetching"), allowing them to view the information ("display", "rendering"), and then access other information ("navigation", "following links").
This process begins when the user inputs a Uniform Resource Locator (URL), for example http://en.wikipedia.org/, into the browser. The prefix of the URL, the Uniform Resource Identifier or URI, determines how the URL will be interpreted. The most commonly used kind of URI starts with http: and identifies a resource to be retrieved over the Hypertext Transfer Protocol (HTTP). Many browsers also support a variety of other prefixes, such as https: for HTTPS, ftp: for the File Transfer Protocol, and file: for computer file. Prefixes that the web browser cannot directly handle are often handed off to another application entirely. For example, mailto: URIs are usually passed to the user's default e-mail application, and news: URIs are passed to the user's default newsgroup reader.
In the case of http, https, file, and others, once the resource has been retrieved the web browser will display it. HTML and associated content (image files, formatting information such as CSS, etc.) is passed to the browser's layout engine to be transformed from markup language to an interactive document, a process known as "rendering". Aside from HTML, web browsers can generally display any kind of content that can be part of a web page. Most browsers can display images, audio, video, and XML files, and often have plug-ins to support Adobe Flash applications and Java applets. Upon encountering a file of an unsupported type or a file that is set up to be downloaded rather than displayed, the browser prompts the user to save the file to disk.
Information resources may contain hyperlinks to other information resources. Each link contains the URI of a resource to go to. When a link is clicked, the browser navigates to the resource indicated by the link's target URI, and the process of bringing content to the user begins again.
All major web browsers allow the user to open multiple information resources at the same time, either in different browser windows or in different tabs of the same window. Major browsers also include pop-up blockers to prevent unwanted windows from "popping up" without the user's consent.
Most web browsers can display a list of web pages that the user has bookmarked so that the user can quickly return to them. Bookmarks are also called "Favorites" in Internet Explorer. In addition, all major web browsers have some form of built-in web feed News aggregator. In Firefox, web feeds are formatted as "live bookmarks" and behave like a folder of bookmarks corresponding to recent entries in the feed. In Opera, a more traditional feed reader is included which stores and displays the contents of the feed.
Furthermore, most browsers can be extended via plug-ins, downloadable components that provide additional features.
Major browsers also possess incremental find features to search within a web page.