Favicon

A favicon (/ˈfæv.ɪˌkɒn/; short for favorite icon), also known as a shortcut icon, website icon, tab icon, URL icon, or bookmark icon, is a file containing one or more small icons,[1] associated with a particular website or web page.[1][2] A web designer can create such an icon and upload it to a website (or web page) by several means, and graphical web browsers will then make use of it.[3] Browsers that provide favicon support typically display a page's favicon in the browser's address bar (sometimes in the history as well) and next to the page's name in a list of bookmarks.[3] Browsers that support a tabbed document interface typically show a page's favicon next to the page's title on the tab, and site-specific browsers use the favicon as a desktop icon.[1]

Wikipedia's favicon, shown in an older version of Firefox (from 2008)

History

In March 1999, Microsoft released Internet Explorer 5, which supported favicons for the first time.[4] Originally, the favicon was a file called favicon.ico placed in the root directory of a website. It was used in Internet Explorer's favorites (bookmarks) and next to the URL in the address bar if the page was bookmarked.[5][6][7][4] A side effect was that the number of visitors who had bookmarked the page could be estimated by the requests of the favicon. This side effect no longer works, as all modern browsers load the favicon file to display in their web address bar, regardless of whether the site is bookmarked.[6]

Standardization

The favicon was standardized by the World Wide Web Consortium (W3C) in the HTML 4.01 recommendation, released in December 1999, and later in the XHTML 1.0 recommendation, released in January 2000.[8][9] The standard implementation uses a link element with a rel attribute in the <head> section of the document to specify the file format and file name and location. Unlike in the prior scheme, the file can be in any Web site directory and have any image file format.[10][11]

In 2003, the .ico format was registered by a third party with the Internet Assigned Numbers Authority (IANA) under the MIME type image/vnd.microsoft.icon.[12][13] However, when using the .ico format to display as images (e.g. not as favicon), Internet Explorer cannot display files served with this standardized MIME type.[13] A workaround for Internet Explorer is to associate .ico with the non-standard image/x-icon MIME type in Web servers.[14]

RFC 5988 established an IANA link relation registry,[15] and rel="icon" was registered in 2010 based on the HTML5 specification. The popular <link rel="shortcut icon" type="image/png" href="image/favicon.png"> theoretically identifies two relations, "shortcut" and "icon", but "shortcut" is not registered and is redundant. In 2011 the HTML living standard[16] specified that for historical reasons "shortcut" is allowed immediately before "icon";[17] however, "shortcut" does not have a meaning in this context.

Legacy

Internet Explorer 5–10 supports only the ICO file format. Netscape 7 and Internet Explorer versions 5 and 6 display the favicon only when the page is bookmarked, and not simply when the pages are visited as in later browsers.[4]

Browser implementation

The following tables illustrate support of various features with major web browsers. Unless noted, the version numbers indicate the starting version number of a supported feature.

File format support

The following table illustrates the image file format support for the favicon.

Browser image file format
ICO PNG GIF animated GIFs JPEG APNG SVG
Edge Yes Yes Yes No Un­known Un­known Un­known
Firefox 1.0[18] 1.0[18] 1.0[18] Yes[19] Yes 3.0[19] 41.0[20]
Google Chrome Yes Yes 4.0 No[21][22] 4.0 No 80[23]
Internet Explorer 5.0[24] 11.0[25] 11.0[25] No[24] No[24] No[24] No[26]
Opera 7.0[27] 7.0[27] 7.0[27] 7.0[27] 7.0[27] 9.5 44.0[28]
Safari Yes 4.0 4.0 No 4.0 No Non-standard (12.0)[lower-alpha 1][29][30]
  1. Safari, since version 12.0, supports single-color SVG favicons in some cases in a non-standard mask-icon format.

Additionally, such icon files can be 16×16, 32×32, 48×48, or 64×64 pixels in size, and 8-bit, 24-bit, or 32-bit in color depth.[1][3] The ICO file format article explains the details for icons with more than 256 colors on various Microsoft Windows platforms.

Use of favicon

This table illustrates the different areas of the browser where favicons can be displayed.

Browser Address bar Address bar drop down list Links bar Bookmarks Tabs Drag to desktop
Edge No Yes Yes Yes Yes Yes
Firefox 1.0–12.0: Yes[31]
> v13: No[32]		 Yes Yes Yes[31] Yes[31] Yes[31]
Google Chrome No[31] No Yes[31] Yes[31] 1.0[31] No[31]
Internet Explorer 7.0[31] No 5.0[31] 5.0[31] 7.0[31] 5.0[31]
Opera 7.0–12.17: Yes
> v14: No[31]		 No 7.0[31] 7.0[31] 7.0[31] 7.0[31]
Safari Yes[31] Yes No[31] Yes[31] 1.0–8.0: Yes
9.0–11.0: No
> 12.0: Optional[33]		 No[31]

Opera Software added the ability to change the favicon in the Speed Dial in Opera 10.[34]

How to use

This table illustrates the different ways the favicon can be recognized by the web browser. The standard implementation uses a link element with a rel attribute in the <head> section of the document to specify the files format, name and location.

Edge Firefox Google Chrome Internet Explorer Opera Safari
<link rel="shortcut icon"
 href="https://example.com/myicon.ico">
Yes[4] Yes[4] Yes[4] Yes[4][24] Yes[4] Yes
<link rel="icon"
 type="image/vnd.microsoft.icon"
 href="https://example.com/image.ico">
Yes Yes Yes Yes (from IE 9)[25] Yes Yes
<link rel="icon" type="image/x-icon"
 href="https://example.com/image.ico">
Yes[4] Yes[4] Yes[4] Yes (from IE 9)[35] Yes[4] Yes
<link rel="icon"
 href="https://example.com/image.ico">
Yes Yes Yes Yes (from IE 11)[25] Yes Yes
<link rel="icon" type="image/gif"
 href="https://example.com/image.gif">
Yes Yes Yes Yes (from IE 11)[25] Yes Yes
<link rel="icon" type="image/png"
 href="https://example.com/image.png">
Yes Yes Yes Yes (from IE 11)[25] Yes Yes
<link rel="icon" type="image/svg+xml"
 href="https://example.com/image.svg">
Yes Yes Yes Yes Yes No
<link rel="mask-icon"
 href="https://example.com/image.svg" color="red">
No No No No No Yes[36]
favicon.ico located in the website's root Yes Optional[lower-alpha 1] Yes Yes Optional[lower-alpha 2] Yes
precedence: prefer root or (X)HTML linked version linked[31] linked[31] linked[31] linked[31] ? ?
  1. Firefox only accepts favicon.ico in the website's root without a <link> tag if the setting browser.chrome.site_icons is set to true in about:config. The default value is true. If set to false, these favicons are ignored.
  2. Opera loads /favicon.ico only if Multimedia/Always load favicon option in opera:config is set to 1. See Opera Support page for more details.

If links for both PNG and ICO favicons are present, PNG-favicon-compatible browsers select which format and size to use as follows. Firefox and Safari will use the favicon that comes last. Chrome for Mac will use whichever favicon is ICO formatted, otherwise the 32×32 favicon. Chrome for Windows will use the favicon that comes first if it is 16×16, otherwise the ICO. If none of the aforementioned options are available, both Chromes will use whichever favicon comes first, exactly the opposite of Firefox and Safari. Indeed, Chrome for Mac will ignore the 16×16 favicon and use the 32×32 version, only to scale it back down to 16×16 on non-retina devices. Opera will choose from any of the available icons completely at random.[37]

Only SeaMonkey does not fetch favicon.ico files in the website's root by default.[38]

Device support

For Apple devices with the iOS operating system version 1.1.3 or later, as well as some Android devices,[39] it is possible to provide a custom icon that users can display on their home screens by using the Add to Home Screen button within the share sheet in Safari.[40][41] This feature is enabled by supplying a <link rel="apple-touch-icon" ...> in the <head> section of documents served by the website. If the custom icon is not provided, a thumbnail of the web page will be put on the home screen instead.[42]

The recommended basic size for this icon is 152×152 pixels.[43]

For the iPad, the basic size is 180x180 pixels. Android tablets [via Chrome] prefer a 192x192 PNG icon.[44]

The icon file referenced by apple-touch-icon is modified to add rounded corners. On the iOS versions prior to iOS 7, a drop shadow, and reflective shine would be added, and apple-touch-icon-precomposed icon may be provided to instruct devices not to apply reflective shine on the image.[41][42]

With rounded corners, added by iOS
<link rel="apple-touch-icon" href="https://example.com/image.png">

No HTML is required by browsers or mobile devices to retrieve these icons, either.[42] The website's root is the default location for the file apple-touch-icon.png (in order of priority).[41][42]

HTML5 recommendation for icons in multiple sizes

The current HTML5 specification recommends specifying multiple sizes for the icons, using the attributes rel="icon" sizes="space-separated list of icon dimensions" within a <link> tag.[45] Multiple icon formats, including container formats such as Microsoft .ico and Macintosh .icns files, as well as Scalable Vector Graphics may be provided by including the icon's content type in the format type="file content-type" within the <link> tag.

As of iOS 5, Apple mobile devices ignore the HTML5 recommendation and instead use the proprietary apple-touch-icon method detailed above. The Google Chrome web browser however, will select the closest matching size from those provided in the HTML headers to create 128×128 pixel application icons, when the user chooses the Create application shortcuts... from the "Tools" menu.

Animated favicons

Various browsers such as Chrome, Firefox and Opera support animation of favicons. A bug report has been open for Firefox since 2001 requesting a way to disable the feature.[46][47]

Limitations and criticism

Due to the need to always check for it in a fixed location, the favicon can lead to artificially slow page-load time and unnecessary 404 entries in the server log if it is nonexistent.[6]

The W3C did not standardize the rel-attribute, so there are other keywords such as shortcut icon that are also accepted by the user agent.[11][24]

Favicons are often manipulated as part of phishing or eavesdropping attacks against HTTPS webpages. Many web browsers display favicons near areas of the web browser's UI, such as the address bar, that are used to convey whether the connection to a website is using a secure protocol like TLS. By changing the favicon to a familiar padlock image an attacker can attempt to trick the user into thinking they are securely connected to the proper website. Automated man-in-the-middle attack tools such as SSLStrip utilize this trick.[48] In order to eliminate this, some web browsers display the favicon within the tab whilst displaying the security status of the protocol used to access the website beside the URL.[49]

Since favicons are usually located at the root of the site directory on the server, they can be employed with some reliability to disclose whether a web client is logged into a given service. This works by making use of the redirect-after-login feature of many websites, by querying for the favicon in a redirect-after-login URL and testing the server response to discern whether the user is given the requested resource (which means they are logged in), or instead redirected to the login page (which means that they are not logged into the service).[50]

References
  1. Lane, Dave (9 August 2008). "Creating a Multi-Resolution Favicon Including Transparency with the GIMP". Egressive.com. Archived from the original on 25 December 2010. Retrieved 25 February 2011.
  2. "What's With Google's New Mini Icon?". BBC. 20 January 2009. Retrieved 25 February 2011. That 16x16 pixel square is the size of the favicon in question, if not the scope.
  3. Apple, Jennifer. "Favicon — How To Create A Favicon.ico". Photoshopsupport.com. Retrieved 25 February 2011.
  4. "How to Add a Shortcut Icon to a Web Page". Microsoft Developer Network. Microsoft. Retrieved 15 March 2010.
  5. McGrew, Darin (26 April 2007). "Web Authoring FAQ – 8.11. How can I have a custom icon when people bookmark my site?". htmlhelp.com. Retrieved 23 February 2011.
  6. Heng, Christopher (7 September 2008). "What is Favicon.ico? Personalise Your Site's Bookmarks". thesitewizard.com. Retrieved 23 February 2011.
  7. "Creating favicons with Adobe Photoshop and GoLive". Adobe GoLive. Archived from the original on 7 December 2003. Retrieved 25 February 2011.
  8. "HTML 4.01 Specification". World Wide Web Consortium. 24 December 1999. Retrieved 14 March 2011.
  9. "XHTML™ 1.0: The Extensible HyperText Markup Language". World Wide Web Consortium. 26 January 2000. Retrieved 14 March 2011.
  10. Dubost, Karl (October 2005). "Web site meta data profile: favicon, ..." World Wide Web Consortium. Retrieved 23 February 2011.
  11. Dubost, Karl (24 October 2005). "How to Add a Favicon to your Site". World Wide Web Consortium. Retrieved 25 February 2011.
  12. Butcher, Simon (3 September 2003). "Published specification". Internet Assigned Numbers Authority. Retrieved 25 February 2011.
  13. "IE9 RC Minor Changes List". IEInternals. Retrieved 7 April 2016.
  14. Irish, Paul (15 December 2010). "commit 37b5fec090d00f38de64 to paulirish's html5-boilerplate". GitHub. Retrieved 25 February 2011.
  15. "Link Relations". IANA.
  16. Ian Hickson (19 January 2011). "HTML is the new HTML5". The WHATWG Blog. WHATWG.
  17. "HTML5 revision r6404". HTML5 Tracker.
  18. David (19 July 2003). "Mozilla 0.9.6 Release Notes". Mozilla. Retrieved 23 February 2011.
  19. "Bug 111373: don't allow animated site icons (favicons)". Retrieved 1 June 2014.
  20. Daniel Holbert (12 June 2015). "Bug 366324 – SVG site icons (favicons, shortcut icons) support – comment 55". Bugzilla@Mozilla. Mozilla. Retrieved 12 June 2015.
  21. tracker, chromium. "no movement in favicon". chromium.org. Retrieved 11 April 2016.
  22. tracker, chromium. "Animated Favicons not supported". chromium.org. Retrieved 8 November 2018.
  23. "Support for SVG in favicons - Chrome Platform Status". 19 November 2019. Retrieved 16 January 2020.
  24. Davis, Jeff (27 December 2007). "why doesn't the favicon for my site appear in IE7?". jeffdav on code. Microsoft. Retrieved 11 March 2013.
  25. "Fun with Favicons". Microsoft. 7 September 2013. Retrieved 3 November 2013.
  26. "SVG favicon support". Microsoft Connect. 3 May 2013. Retrieved 4 September 2014.
  27. "Opera 7 for Windows Changelog". Opera Software. 28 January 2003. Retrieved 28 February 2011.
  28. "What's new in Opera". Opera Software. Retrieved 24 June 2017.
  29. "Safari Technology Preview 58, with Safari 12 Features, is Now Available". WebKit. 6 June 2018. Retrieved 3 March 2019.
  30. "Favicons. Finally". Iconfactory. 7 June 2018. Retrieved 3 March 2019.
  31. Francis, Lewis (11 December 2007). "Chart of modern browser support for favicon". informationgift.com. Retrieved 23 February 2011.
  32. "Firefox deems favicons risky, banishes them from address bar". Engadget. Retrieved 10 September 2012.
  33. "How to enable favicons in Safari so you can identify websites in tabs graphically". iDownloadBlog. 14 June 2018. Retrieved 14 October 2020.
  34. "Opera 10.0 beta 2 for Windows changelog". Opera Software. 16 July 2009. Retrieved 27 February 2011.
  35. "IE9 RC Minor Changes List". Microsoft. 11 February 2011. Retrieved 16 November 2013.
  36. "Creating Pinned Tab Icons". Apple Inc. 12 December 2016. Retrieved 9 April 2019.
  37. Jonathan T. Neal (16 January 2013). "Understand the Favicon". Archived from the original on 23 May 2013. Retrieved 30 May 2013.
  38. Mathias Bynens (14 April 2010). "rel="shortcut icon" considered harmful". Retrieved 15 November 2011.
  39. Mathias Bynens (2 March 2011). "Everything you always wanted to know about touch icons". Retrieved 15 November 2011.
  40. "iPhone Human Interface Guidelines for Web Applications: Metrics, Layout Guidelines, and Tips". Apple Inc. Retrieved 27 May 2010.
  41. "Safari Web Content Guide: Specifying a Webpage Icon for Web Clip". Apple Inc. 15 November 2010. Retrieved 25 February 2011.
  42. McLellan, Drew (17 January 2008). "How To Set an Apple Touch Icon for Any Site". Allinthe head.com. Retrieved 11 March 2011.
  43. "Apple-touch-icon". Apple Inc. Retrieved 9 April 2019.
  44. "Android Chrome and its favicon". Retrieved 9 September 2014.
  45. "HTML Living Standard, Section 4.6.6.6 'Link type "icon"'". WHATWG. Retrieved 17 November 2015.
  46. "Bug 111373 - don't allow animated site icons (favicons)". bugzilla.mozilla.org. 21 November 2001.
  47. "Firefox Bug 111373 - don't allow animated site icons (mozilla.org)". Hacker News. 7 July 2015.
  48. Marlinspike, Moxie (21 February 2011). "Defeating Ssl Using Sslstrip (Marlinspike Blackhat)". (see description of video). SecurityTube. Archived from the original on 13 July 2011. Retrieved 9 July 2011.
  49. "Firefox version 14 features". Retrieved 18 July 2012.
  50. Linus, Robin. "Your Social Media Fingerprint". Retrieved 14 October 2016.
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