The view-source URI scheme is used by some browsers to construct URLs

Uniform Resource Locator

In computing, a uniform resource locator or universal resource locator is a specific character string that constitutes a reference to an Internet resource....

 that refer to a source display for a given resource.

For example, this URI

Uniform Resource Identifier

In computing, a uniform resource identifier is a string of characters used to identify a name or a resource on the Internet. Such identification enables interaction with representations of the resource over a network using specific protocols...

 would show the source of the page located at http://www.example.com:
view-source:http://www.example.com

On 25 May 2011 the 'view-source' URI scheme was officially registered with IANA per RFC 4395.

Browser Support

Mozilla Firefox

Mozilla Firefox

Mozilla Firefox is a free and open source web browser descended from the Mozilla Application Suite and managed by Mozilla Corporation. , Firefox is the second most widely used browser, with approximately 25% of worldwide usage share of web browsers...

 and Internet Explorer

Internet Explorer

Windows Internet Explorer is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems, starting in 1995. It was first released as part of the add-on package Plus! for Windows 95 that year...

 both supported the scheme, but support was dropped from Internet Explorer in Windows XP

Windows XP

Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...

 SP2 due to security problems. Firefox also suffered a similar security issue (by combining view-source and javascript URIs), but still supported it in Firefox 1.5 after being fixed. In 2009 a new discovered bug was fixed in Firefox 3.0.9

Mozilla Firefox 3

Mozilla Firefox 3.0 is a version of the Firefox web browser released on June 17, 2008 by the Mozilla Corporation.Firefox 3.0 uses version 1.9 of the Gecko layout engine for displaying web pages. This version fixes many bugs, improves standard compliance, and implements many new web APIs compared to...

.

• Mozilla Firefox - supported
• View Source Choice - a Mozilla Firefox extension that adds more options.
• Netscape
  Netscape
  Netscape Communications is a US computer services company, best known for Netscape Navigator, its web browser. When it was an independent company, its headquarters were in Mountain View, California...
  
   - supported
• Internet Explorer 4
  Internet Explorer 4
  Microsoft Internet Explorer 4 is a graphical web browser released in September 1997 by Microsoft, primarily for Microsoft Windows, but also with versions available for Apple Mac OS, Solaris, and HP-UX and marketed as "The Web the Way You Want It".It was one of the main participants of the first...
  
  , 5
  Internet Explorer 5
  Microsoft Internet Explorer 5 was a graphical web browser released in March 1999 by Microsoft, primarily for Microsoft Windows, but initially with versions available for Apple Macintosh, Sun Solaris, and HP-UX. It was one of the main participants of the first browser war...
  
  , and 6
  Internet Explorer 6
  Internet Explorer 6 is the sixth major revision of Internet Explorer, a web browser developed by Microsoft for Windows operating systems...
  
   - supported
• Internet Explorer 6
  Internet Explorer 6
  Internet Explorer 6 is the sixth major revision of Internet Explorer, a web browser developed by Microsoft for Windows operating systems...
  
  , 7
  Internet Explorer 7
  Windows Internet Explorer 7 is a web browser released by Microsoft in October 2006. Internet Explorer 7 is part of a long line of versions of Internet Explorer and was the first major update to the browser in more than 5 years...
  
  , and 8
  Internet Explorer 8
  Windows Internet Explorer 8 is a web browser developed by Microsoft in the Internet Explorer browser series. The browser was released on March 19, 2009 for Windows XP, Windows Server 2003, Windows Vista, Windows Server 2008, and Windows 7. Both 32-bit and 64-bit builds are available...
  
   - not supported after Windows XP SP2
• Safari
  Safari (web browser)
  Safari is a web browser developed by Apple Inc. and included with the Mac OS X and iOS operating systems. First released as a public beta on January 7, 2003 on the company's Mac OS X operating system, it became Apple's default browser beginning with Mac OS X v10.3 "Panther". Safari is also the...
  
   3.2.1 - supported
• Opera
  Opera (web browser)
  Opera is a web browser and Internet suite developed by Opera Software with over 200 million users worldwide. The browser handles common Internet-related tasks such as displaying web sites, sending and receiving e-mail messages, managing contacts, chatting on IRC, downloading files via BitTorrent,...
  
   7, 8, 9, 10, 11 - not supported
• Google Chrome
  Google Chrome
  Google Chrome is a web browser developed by Google that uses the WebKit layout engine. It was first released as a beta version for Microsoft Windows on September 2, 2008, and the public stable release was on December 11, 2008. The name is derived from the graphical user interface frame, or...
  
   - supported
• Epiphany - supported
• HP webOS - supported in-browser via a homebrew app called Internalz Pro