These are some of the features of Mozilla Firefox that distinguish it from other web browsers such as Internet Explorer. In an effort to combat interface bloat and to allow the browser to be shipped as a small, pared-down core easily customizable to meet individual users' needs, Firefox relies on the extension system to allow users to modify the browser according to their requirements instead of providing all features in the standard distribution.

Web technologies support

Main article: Gecko (layout engine)

Firefox supports most basic Web standards including HTML, XML, XHTML, CSS (with extensions[1]), JavaScript, DOM, MathML, SVG, XSLT and XPath.[2] Firefox's standards support and growing popularity have been credited as one reason Internet Explorer 7 was to be released with improved standards support.[3]

Since Web standards are often in contradiction with Internet Explorer's behavior, Firefox, like other browsers, has a quirks mode. This mode attempts to mimic Internet Explorer quirk modes, which equates to using obsolete rendering standards dating back to Internet Explorer 5, or alternately newer peculiarities introduced in IE 6 or 7.[4] However, it is not completely compatible.[5] Because of the differing rendering, PC World notes that a minority of pages do not work in Firefox,[6] however Internet Explorer 7 quirk mode does not either. [4]

CNET notes that Firefox does not support ActiveX controls by default, which can also cause webpages to be missing features or to not work at all in Firefox.[7] Mozilla made the decision to not support ActiveX due to potential security vulnerabilities, its proprietary nature and its lack of cross-platform compatibility.[8][9][10] There are methods of using ActiveX in Firefox such as via third party plugins but they do not work in all versions of Firefox or on all platforms.[11]

Beginning on December 8, 2006, Firefox trunk nightly builds pass the Acid2 CSS standards compliance test, so all future releases of Firefox 3 will pass the test.[12]

Firefox also implements[13] a proprietary protocol[14] from Google called "safebrowsing", which is not an open standard.

Cross-platform support

Unsupported versions for old operating systems Version
Mac OS X
v10.1 1.0.8
v10.4-10.6 3.6.28 [15]
OS/2 and eComStation 3.5.4 [16]
NT 4/98/ME
2000 12.0 and 10.0.12esr

Mozilla Firefox runs on certain platforms that coincide OS versions in use at the time of release. In 2004 version 1 supported older operating systems such as Windows 95 and Mac OS X 10.1, by 2008 version 3 required at least OS X 10.4 and even Windows 98 support ended.

Various releases available on the primary distribution site can support the following operating systems, although not always the latest Firefox version.

Builds for Solaris (x86 and SPARC), contributed by the Sun Beijing Desktop Team, are available on the Mozilla web site.[17]

Mozilla Firefox 1.x installation on a few additional steps.

Since Firefox is open source and Mozilla actively develops a platform independent abstraction for its graphical front end, it can also be compiled and run on a variety of other architectures and operating systems. Thus, Firefox is also available for many other systems. This includes OS/2, AIX, and FreeBSD. Builds for Windows XP Professional x64 Edition are also available. Mozilla Firefox is also the browser of choice for a good number of smaller operating systems, such as SkyOS and ZETA.

Firefox uses the same profile format on the different platforms, so a profile may be used on multiple platforms, if all of the platforms can access the same profile; this includes, for example, profiles stored on an NTFS (via FUSE) or FAT32 partition accessible from both Windows and Linux, or on a USB flash drive. This is useful for users who dual-boot their machines. However, it may cause a few problems, especially with extensions.

Aero peek capability

Mozilla has included aero peek capability for each tab on Windows 7. This feature was previously not enabled by default (but can be user enabled), but now is included as a full feature of Firefox. This resulting in a displayed thumbnail image of the tab. This will create similar functioning to that which is already included in IE8.


Firefox includes many features designed to improve security. Key features include a cookies.

Firefox is open source software, and thus, its source code is visible to everyone. This allows anyone to review the code for security vulnerabilities, whether their intentions are good or malicious.[18] It also allowed the U.S. Department of Homeland Security to give funding for the automated tool Coverity to be run against Firefox code.[19]

Additionally, Mozilla has a security bug bounty system - anyone who reports a valid critical security bug receives a $3000 (US) cash reward for each report and a Mozilla T-shirt.[20] With effect from December 15, 2010 Mozilla added Web Applications to its Security Bug Bounty Program.[21][22]

Tabbed browsing

Firefox supports MultiZilla extension for Mozilla.

Firefox also permits the "homepage" to be a list of URLs delimited with vertical bars (|), which are automatically opened in separate tabs, rather than a single page.

Firefox 2 supports more tabbed browsing features, including a "tab overflow" solution that keeps the user's tabs easily accessible when they would otherwise become illegible, "session store" which lets the user keep the opened tabs across the restarts, and an "undo close tab" feature.

Pop-up blocking

Firefox also includes integrated customizable pop-up blocking. Firefox was given this feature early in beta development, and it was a major comparative selling point of the browser until Internet Explorer gained the capability in the Windows XP SP2 release of August 25, 2004. Firefox's pop-up blocking can be turned off entirely to allow pop-ups from all sites. Firefox's pop-up blocking can be inconvenient at times — it prevents JavaScript-based links opening a new window while a page is loading unless the site is added to a "safe list" found in the options menu.

In many cases it is possible to view the pop-up's URL by clicking the dialog that appears when one is blocked. This makes it easier to decide if the pop-up should be displayed.

Private Browsing

Private Browsing, also known popularly as "Porn Mode", is a recent feature inclusion in Mozilla Firefox. It was introduced in Firefox 3.5, which released on June 30, 2009. This feature lets users browse the Internet without leaving any traces in the browsing history.

Download manager

An integrated customizable download manager is also included. Downloads can be opened automatically depending on the file type, or saved directly to disk. By default, Firefox downloads all files to a user's desktop on Mac and Windows or to the user's home directory on Linux, but it can be configured to prompt for a specific download location. Version 3.0 added support for cross-session resuming (stopping a download and resuming it after closing the browser). From within the download manager, a user can view the source URL from which a download originated as well as the location to which a file was downloaded.

Live bookmarks

Powered by RSS or Atom feeds, "Live Bookmarks", allow users to dynamically monitor changes to their favorite news sources. When this feature was first introduced in version 1.0 PR, there were a few worries that Firefox was beginning to include non-essential features and that it was beginning to bloat the browser much like the Mozilla Suite[1].

Instead of treating RSS-feeds as HTML pages like most news aggregators do, they are treated as bookmarks that are updated in real-time with a link to the appropriate source. Live bookmarks are updated automatically; however no browser option exists to prevent or control the automatic Live Bookmark updates.

Other features

Find as you type

Firefox also has an incremental find feature known as "Find as you type", invoked by pressing Ctrl+F. With this feature enabled, a user can simply begin typing a word while viewing a web page, and Firefox automatically searches for it and highlights the first instance found. As the user types more of the word, Firefox refines its search. Also, if the user's exact query does not appear anywhere on the page, the "Find" box turns red. Ctrl+G can be pressed to go to the next found match. Alternatively the slash (/) key can be used instead to invoke the "quick search". The "quick search", in contrast to the normal search, lacks search controls and is wholly controlled by keyboard. In this mode highlighted links can be followed by pressing the enter key. The "quick search" has an alternate mode which is invoked by pressing the apostrophe (') key, in this mode only links are matched.

Mycroft Web Search

A built-in Mycroft Web search function features extensible search-engine listing; by default, Firefox includes plugins for Google and Yahoo!, and also includes plugins for looking up a word on and browsing through listings. Other popular Mycroft search engines include World Heritage Encyclopedia, eBay, and IMDb.

Smart Bookmarks

Smart Bookmarks (aka Smart keywords) can be used to quickly search for information on specific Web sites.[23] A smart keyword is defined by the user and can be associated with any bookmark, and can then be used in the address bar as a shortcut to quickly get to the site or, if the smart keyword is linked to a searchbox, to search the site. For example, "imdb" is a pre-defined smart keyword; to search for information about the movie 'Firefox' on IMDb, jump to the location bar with the CTRL+L shortcut, type "imdb Firefox" and press the Enter key or just simply type in "imdb" if one wants to get to the frontpage instead.


The chrome packages within Firefox control and implement the Firefox user interface.[24]

Version 2.0 and above

Main article: Mozilla Firefox 2

Enhanced search capabilities

Search term suggestions will now appear as users type in the integrated search box when using the Google, Yahoo! or search engines. A new search engine manager makes it easier to add, remove and re-order search engines, and users will be alerted when Firefox encounters a website that offers new search engines that the user may wish to install.


Support for Microsummaries was added in version 2.0. Microsummaries are short summaries of web pages that are used to convey more information than page titles. Microsummaries are regularly updated to reflect content changes in web pages so that viewers of the web page will want to revisit the web page after updates. Microsummaries can either be provided by the page, or be generated by the processing of an XSLT stylesheet against the page. In the latter case, the XSLT stylesheet and the page that the microsummary applies to are provided by a microsummary generator. Support for Microsummaries was removed as of Firefox 6. [25]

External links:

  • Microsummaries - MozillaWiki

Live Titles

When a website offers a

Session Restore

The Session Restore feature restores windows, tabs, text typed in forms, and in-progress downloads from the last user session. It will be activated automatically when installing an application update or extension, and users will be asked if they want to resume their previous session after a system crash.

Inline spell checker

A built-in spell checker enables users to quickly check the spelling of text entered into Web forms without having to use a separate application.

Usability in version 2

Firefox 2 was designed for the average user, hiding advanced configuration and making features that do not require user interaction to function.[27] Jim Repoza of eWEEK states[28] Template:Cquote Firefox also won UK Usability Professionals' Association's 2005 award for "Best software application".[29]

Version 3.0 and above

Main article: Mozilla Firefox 3

Star button

Quickly add bookmarks from the location bar with a single click; a second click lets the user file and tag them.


Smart Location Bar

Firefox 3 includes a "Smart Location Bar". While most other browsers, such as Internet Explorer, will search through history for matching web sites as the user types a URL into the location bar, the Smart Location Bar will also search through bookmarks for a page with a matching URL. Additionally, Firefox's Smart Location Bar will also search through page titles, allowing the user to type in a relevant keyword, instead of a URL, to find the desired page.


View, organize and search through bookmarks, tags and browsing history using the new Library window. Create or restore full backups of this data whenever with a few clicks.

Smart Bookmark Folders

Users can quickly access their most visited bookmarks from the toolbar, or recently bookmarked and tagged pages from the bookmark menu. Smart Bookmark Folders can be created by saving a search query in the Library.

Full page zoom

From the View menu and via keyboard shortcuts, the new zooming feature lets users zoom in and out of entire pages, scaling the layout, text and images, or optionally only the text size. Zoom settings will be remembered for each site.

Text selection improvements

In addition to being able to double-click and drag to select text by words; or triple-click and drag to select text by paragraph. Ctrl (Cmd on Mac) can be held down to retain the previous selection and extend it instead of replacing it when doing another selection. [30]

Web-based protocol handlers

Web applications, such as a user's favorite webmail provider, can now be used instead of desktop applications for handling mailto: links from other sites. Similar support is available for other protocols (Web applications will have to first enable this by registering as handlers with Firefox).

Add-ons and extensions

There are four types of add-ons in Firefox: extensions, themes, language packs and plugins. Firefox add-ons may be obtained from the Mozilla Add-ons web site or from other sources.


Firefox users can add features and change functionality in Firefox by installing extensions. Extension functionality is varied; such as those enabling mouse gestures, those that block advertisements, and those that enhance tabbed browsing.

Features that the Firefox developers believe will be used by only a small number of its users are not included in Firefox, but instead left to be implemented as extensions.MultiZilla was an extension that provided tabbed browsing when Mozilla lacked that feature.

While extensions provide a high level of customizability, PC World notes the difficulty a casual user would have in finding and installing extensions as compared to their features being available by default.[6]

Most extensions are not created or supported by Mozilla. Extensions have the same rights to the user's system as Firefox itself, and malicious extensions have been created.[32] Mozilla provides a repository of extensions that have been reviewed by volunteers and are believed to not contain malware. Since extensions are mostly created by third parties, they do not necessarily go through the same level of testing as official Mozilla products, and they may have bugs or vulnerabilities.[33]


Firefox also supports a variety of themes for changing its appearance. Themes are simply packages of CSS and image files. Many themes can be downloaded from the Mozilla Update web site.

Language packs

Language packs are dictionaries for spell checking of input fields.


Firefox supports plugins based on Netscape Plugin Application Program Interface (NPAPI), i.e. Netscape-style plugins. As a side note, Opera and Internet Explorer 3.0 to 5.0 also support NPAPI.

On June 30, 2004, the Mozilla Foundation, in partnership with richer web browsing experiences, helping to maintain innovation and standards. The new plugin technologies are expected to be implemented in the future versions of the Mozilla applications.

Mozilla Firefox 1.5 and later versions include the Java Embedding plugin,[34] which allow Mac OS X users to run Java applets with the latest 1.4 and 5.0 versions of Java (the default Java software shipped by Apple is not compatible with any browser, except its own Safari).


Beyond the use of Add-ons, Firefox additional customization features.

  • The position of the toolbars and interface are customizable
  • User stylesheets to change the style of webpages and Firefox's user interface.

A number of internal configuration options are not accessible in a conventional manner through Firefox's preference dialogs, although they are exposed through its about:config interface.


External links

  • Firefox Features at
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