General concepts

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This article lists some common terms and general concepts found in articles about Mozilla applications.


Bugzilla is a system designed by Mozilla developers to track bugs in Mozilla software. Bugzilla is also a free, open-source Mozilla product used by many other companies, organizations and projects to manage software development.


Most major versions of Mozilla software have internal project names or "codenames". Each time Mozilla developers decide to create the next major software version, it is split from the main development tree (in a process called "branching") and is given a codename to differentiate the new product from other versions, before being officially named, numbered, and released. For example, "Deer Park" was the codename for Firefox 1.5, "Bon Echo" is the codename for Firefox 2 development and "Minefield" is the codename for the trunk (main development branch) which will eventually become Firefox 3. "Lightning" is the codename for a project working to integrate Thunderbird with calendar functionality. "SeaMonkey", the former codename of Mozilla Suite, has been adopted as the official name for its successor. For more information, see the Internal project names article.


Cascading Style Sheets (CSS) is a stylesheet language used to describe the style of elements (fonts, colors, spacing, etc.) in a web document written in HTML or XML (including various XML languages like XHTML or SVG). In Gecko-based products such as Firefox, Thunderbird and Mozilla Suite, CSS is also used for styling the application's user interface. For example, themes make heavy use of CSS to change the appearance of the application. Additional resources can be found in the CSS section of this article.


HyperText Markup Language (HTML) is a computer language that allows for the creation of web pages viewable in a web browser. It is sometimes also used in e-mail messages for including font colors, images, or other complex formatting. See HTML at Mozilla Developer Center for additional documentation.


Hypertext Transfer Protocol (HTTP) is a communications protocol for requesting and sending documents on the World Wide Web.


Internet Message Access Protocol (IMAP) is a network protocol used to access e-mail messages while they are still stored on the server. IMAP allows a user to access messages stored in remote folders as if it were a local folder. More information on using IMAP mail accounts in Mozilla applications can be found in the IMAP article.


Internet Relay Chat (IRC) is a form of instant communication over the Internet. It wasl developed a long time ago for use with groups in need of a communications mechanism. Mozilla's IRC server is (alternatively attach to moznet network). There are lots of channels there, some of them are:

  • #firefox — Firefox support and Firefox-related chatter.
  • #thunderbird — Same for Thunderbird.
  • #mozillazine — support for the Mozilla Suite.
  • #mozilla — Mozilla development-related support and chatting

A good tutorial can be found on for IRC newbies (people new to IRC).

IRC Clients


Java is a programming language used to create stand-alone software applications (including games). Java programs can also be embedded in webpages, in which case they are called ‘applets’. Java applications and applets require additional software (the Java Runtime Environment) to be installed on your system and should not be confused with "JavaScript" (see below). More information about installing and troubleshooting Java in your Mozilla application can be found in the Java article.


A JavaScript script is usually a small series of commands that are often embedded in a webpage to do things like create fly-out menus, invoke pop-up windows, and validate form data. Support for JavaScript is built into all XUL-based applications such as Firefox, Thunderbird and Mozilla Suite. JavaScript is actually a complete programming language and it is one of the languages in which Mozilla products are written. Note that JavaScript is not Java! These are completely separate technologies. For more information on using JavaScript in your Mozilla application, see the JavaScript article.


MHTML is a proposed Internet standard (RFC2557) for preserving an entire web page and all inline graphics, links, applets etc. In a single file. Although supported by Internet Explorer, it currently remains unimplemented in Mozilla. [1] [2] The MAF extension partially supports MHTML, along with its own method for archiving entire web pages; UnMHT1 is another extension for saving and opening MHT files (MHTML format). For more information on the MHTML file format, see MSDN Library - MIME Encapsulation of Aggregate HTML Documents (MHTML)

MIME types

Mozilla applications use MIME types (content types) to determine how to handle content downloaded from the Internet. MIME types that are handled by installed plugins can be viewed by entering about:plugins in the Location Bar. For example, if the Flash plugin is installed, you would see the application/x-shockwave-flash MIME type for SWF files listed under the "Shockwave Flash" entry or, if QuickTime is installed, you may see the audio/mpeg MIME type for MP3 or other MPEG audio files, listed under the entry for the "QuickTime" plugin. See File types and download actions and Properly Configuring Server MIME Types (MDC) for more information.


Firefox, Thunderbird, and SeaMonkey have release candidates and final versions that are announced on Mozilla and other websites; however, developers check in new code every day to add stability and security fixes, new features or other improvements. The program code is recompiled each night and these nightly builds or "nightlies" are uploaded to Mozilla's servers for testing, to help developers find and fix bugs. Using nightly builds is an excellent way to get involved in Mozilla development and help find, report and triage bugs; however, nightly builds may be unstable so they should be avoided for anything other than testing purposes. More information can be found on the MozillaZine Firefox Builds SeaMonkey Builds and Thunderbird Builds forums.

Quality Feedback Agent

The Quality Feedback Agent (aka Talkback) is a small program that activates when Firefox, Thunderbird or Mozilla Suite crashes. It allows you to send information to Mozilla developers so that they can improve future versions of Mozilla applications. More information can be found in the Quality Feedback Agent article.


RSS ("Really Simple Syndication") is a method that some websites use to provide news or other articles. Some web sites post a lot of new articles which can be difficult to track. While you can always visit your bookmarked sites to see the latest articles it's sometimes more convenient to have new stories sent to you automatically; more so if you have a lot of sites to keep up with. Traditionally, one way around this was via email newsletter.

RSS is a new way to automatically get the latest info you're interested about whether it's new headlines from Yahoo News's Business section, the latest entries from your favorite blogs or even from mozillaZine. RSS pages can be read with Firefox or Thunderbird depending on your browsing preference.


Secure sockets layer (SSL) is a cryptographic protocol used to turn a TCP-IP connection into a secure connection. For example, if you're using a browser it prevents a third party from seeing your credit card number as you type it into the web page.


Scalable Vector Graphics (SVG) is an XML language for sophisticated 2-dimensional graphics. SVG is similar in scope to Macromedia's proprietary Flash technology: among other things it offers anti-aliased rendering, pattern and gradient fills, sophisticated filter-effects, clipping to arbitrary paths, text and animations. What distinguishes SVG from Flash, is that it is a W3 recommendation (i.e. a standard for all intents and purposes) and that it is XML-based as opposed to a closed binary format. It is explicitly designed to work with other W3C standards such as CSS, DOM and SMIL. For example code, see the article, Using SVG with XBL in XUL.

The latest Firefox/Mozilla builds have support for SVG (Scalable Vector Graphics). Older versions of the browser require the Adobe SVG Viewer plugin to view SVG images.


Transport Layer Security (TLS) is a cryptographic protocol used to turn a TCP-IP connection into a secure connection. For example, if you're using a email client it prevents a third party from seeing your password as Thunderbird logs you into the mail server. TLS is basically version 3.0 of SSL with some changes to make it more suitable as a IETF standard. Despite their similarities they're not interoperable.

SSL and TLS are used with both browsers and email clients. Normally a user doesn't know which one is used with their browser, while they have to explicitly configure it with a email client (select "TLS" or "TLS if available" when configuring the account or SMTP server).

User agent

The user agent string is a piece of text which identifies the name and version of a given browser. It can be accessed by javaScript and numerous other means. It is used by websites to determine which browser you use. Some webmasters do this solely for the purpose of keeping statistics on browser usage. Others will deliberately reject certain browsers based on the user agent string, or redirect them to different version of a page.

To see your own user agent string, copy javascript:alert(navigator.userAgent) into the Location Bar and press Enter. Alternately, go to the "Help" menu and select "About Mozilla Firefox" (or other product name) where the user agent string is displayed at the bottom of the dialog box.

If a web site is rejecting access solely based on the user agent string, you may wish to install the User Agent Switcher extension, which allows you to change your user agent string in order to mimic that of other browsers such as Microsoft Internet Explorer. Note that this may cause problems with the Java plugin.