A web browser is application software for accessing . When a user requests a web page from a particular website, the browser retrieves its Computer file from a web server and then displays the page on the user's screen. Browsers are used on a range of devices, including desktop computer, , tablet computer, and . In 2020, an estimated 4.9 billion people used a browser. The most used browser is Google Chrome, with a 65% global market share on all devices, followed by Safari with 18%.
A web browser is not the same thing as a search engine, though the two are often confused. A search engine is a website that provides hyperlink to other websites. However, to connect to a website's server and display its web pages, a user must have a web browser installed. In some technical contexts, browsers are referred to as .
Web pages usually contain to other pages and resources. Each link contains a URL, and when it is clicked or touchscreen, the browser navigates to the new resource. Most browsers use an internal web cache of web page resources to improve loading times for subsequent visits to the same page. The cache can store many items, such as large images, so they do not need to be downloaded from the server again. Cached items are usually only stored for as long as the web server stipulates in its HTTP response messages.
Microsoft debuted Internet Explorer in 1995, leading to a browser war with Netscape. Within a few years, Microsoft gained a dominant position in the browser market for two reasons: it bundled Internet Explorer with Microsoft Windows, their popular operating system and did so as freeware with no restrictions on usage. The market share of Internet Explorer peaked at over 95% in the early 2000s. In 1998, Netscape launched what would become the Mozilla Foundation to create a new browser using the open-source software model. This work evolved into the Firefox browser, first released by Mozilla in 2004. Firefox's market share peaked at 32% in 2010. Apple released its Safari browser in 2003. Safari remains the dominant browser on Apple devices, though it did not become popular elsewhere.
Some alternative browsers have gained prevalence, due to their increased customization and privacy. Some such browsers also have built-in Ad blocking. Examples include Brave, Epic, Maxthon, and Opera. The Tor Browser gives access to the Tor anonymity network. Tor allows access to the dark web, repeatedly encrypting traffic for privacy. The alternative browsers have low market share compared to the large browsers; for example, Opera is the highest alternative browser by a wide margin, at a 2.49% market share in October 2022.
Most browsers have common user interface features such as:
While have similar UI features as desktop computer versions, the limitations of touchscreen require mobile UIs to be simpler. The difference is significant for users accustomed to keyboard shortcuts. The most popular desktop browsers also have sophisticated web development tools.
Breaches of web browser security are usually for the purpose of bypassing protections to display pop-up advertising collecting personally identifiable information (PII) for either Internet marketing or identity theft, website tracking or web analytics about a user against their will using tools such as Web bug, Clickjacking, Likejacking (where Facebook's like button is targeted), HTTP cookie, Zombie cookie or Flash cookies (Local Shared Objects or LSOs); installing adware, Computer virus, spyware such as Trojan horses (to gain access to users' personal computers via cracking) or other malware including online banking theft using man-in-the-browser attacks.