A Firefox Glossary

by Brian King, Firefox Hacks contributor, and coauthor of Creating Applications with Mozilla

Author's note: Thanks to Nigel McFarlane, author of Firefox Hacks, for his technical review and contribution to this glossary.

Firefox is hot! Though the initial wave of enthusiasm has leveled off, Firefox is still gaining in popularity, downloads are still increasing, and Firefox is emerging as a front-running web browser. It is not just a good browser; it has also achieved something else that is more difficult to measure. It has made web browsing fun again and brought new spirit to an arena that had become stale.

With Firefox, the Mozilla Foundation made a U-turn that probably ensured its survival. It started focusing on users, targeting releases directly at them instead of at developers and hardcore power users.

Some companies have started to switch, extension authors have adopted the Mozilla platform for writing their tools and applications, and web developers are being turned on by the high level of web-standards support. This glossary is by no means exhaustive--it is meant to be a teaser to lead you to explore more. Get Firefox Hacks to dig deeper--you'll find references to specific chapters or hacks in the book throughout this glossary.


about:config: This URL provides access to a wealth of configuration preferences (see Chapter 1 of Firefox Hacks) to change how Firefox looks and behaves. Type it in the location bar and away you go. Make sure you know what you are doing.

Alpha blending: The overlaying of text and images using CSS to create a layered effect (see Hack 45). Gecko has very solid CSS support (see Hacks 44-46).

Alphabets: Firefox can display web pages written in every language under the sun, thanks to its robust Unicode support.


Ben and Blake: The cult of personality somewhat surrounds this project, and these folks are the two best-known Firefox developers. Read about them in this Wired article.

Bookmarklets: Fancy bookmarks that execute some code. Instead of placing a URL as the bookmark, add JavaScript and prepend it with the protocol javascript:. Not unique to Firefox, but worth a mention nonetheless.

Building: If you have the right tools in place, it's not so difficult to build Firefox yourself (Hack 93). Worthwhile if you would like to contribute patches, or if you are just interested in learning the code.

Bundling: Pull the Firefox installer apart and put it back together again to suit your requirements (Hack 28).


Caret browsing: Want to navigate a web page like a word-processing document? Just hit F7 and you can step through the page character by character, line by line.

Chrome: Chrome is a term that encompasses anything you see in the UI, including menus, buttons, and status bars. Under the covers, "files in 'chrome'" refers to all files that make up the UI. Special internal chrome URLs (e.g. chrome://browser/content/) allow access to chrome files for registered extensions.

Command-line options: Starting Firefox from a command shell (Hack 10) gives you more control, and allows you to do different things such as start the Profile Manager, set the window width and height, or choose a different locale:

mozilla - UILocale it-IT 

Customize: The look and feel of Firefox is far from static. There are many ways to change it, from minor tweaks (Chapter 7) to installing a full theme. Add or remove a button from the toolbar by right-clicking on it and choosing "Customize...".


Debugging: Firefox has some useful tools for debugging web pages (Hack 55) and extensions. It comes prepackaged with the DOM Inspector and the JavaScript console. Many third-party extensions add extra features.

Download: The Firefox Download Manager lets you track the progress of big file downloads. Firefox can restart paused downloads as long as you don't shut the browser down completely.


Extension Manager: This is the name given to both the front end (UI) and the mechanism as a whole for using extensions in Firefox. The main sources for extensions are Mozilla Update and Currently, extensions are installed into the user profile area, but changes are coming in version 1.1 to allow for more flexible install choices for authors.


Fast: Firefox starts up fast and renders pages fast. There are preference tweaks you can do to try and make it even faster (Hack 9). If startup is slow for you, chances are it is because of extensions that you have installed, but by default after a fresh install, it is very snappy.

Find as you type: Set to off by default, this feature will try to find matches as soon as you type anything when viewing a web page. To turn it on, go to Options -> Advanced -> Accessibility.

Find toolbar: The non-intrusive toolbar pops up at the bottom of the screen to search the page when you hit Ctrl+F or start typing when Find As You Type is on. Hit Enter to go to the next match. A pleasure to use, if you are used to a dialog popping up that requires more interaction.

Figure 1
Figure 1. The Find toolbar with highlighting enabled


Gecko: The content layout engine that powers Firefox.

GreaseMonkey: An extension that is making waves, GreaseMonkey allows you to plug in scripts to modify the look or behavior of a web page.


Hacking: Firefox's extension and theme systems gives incentive for anyone with an idea and the will to learn. Web developers can harness their existing skills with CSS, JavaScript, and mark-up. Want something more involved or you need to hook into third-party C APIs? Write a JavaScript or C++ component (Hack 82).

Help Viewer: The Help -> Help Contents menu item will open the Help Viewer. Along with its content, you can find there a glossary, an index, and search capabilities. Extension authors can utilize the Help Viewer and add their own content in the form of Help Content Packs.


Image blocker: The ability to block images on a per-server basis. Context-click on an image and choose "Block Images from <server>." More image settings are available in Options (Web Features).

Figure 2
Figure 2. Image options on Windows, including blocking

install.rdf: This file is bundled with an extension installer XPI, and tells Firefox everything it needs to know to register the extension (Hack 88).


JAR files: Firefox's UI chrome files are packaged into compressed JAR files mainly to save space. Extension authors have the option to distribute their files compressed like this, or "as is" (Hack 86).

jsLib: A JavaScript utility library that exposes Firefox functionality to extension developers for ease of use in their application. More information is at


Keyboard shortcuts: There are many that are common with other applications, and some that are unique to Firefox. Ctrl+U to view page source, Shift+F3 to find the last search term backwards--Hack 5 has more details.


Livemarks: Also known as live bookmarks, these are bookmark representations of RSS or Atom feeds. They display as a folder in the user-chosen location in bookmarks, and expand to include all headlines for the feed. Ideal for keeping up with news and blogs. You can add one easily by clicking on the Add Livemark icon Livemark in the status bar when it appears for a page.

Related Reading

Firefox Hacks
Tips & Tools for Next-Generation Web Browsing
By Nigel McFarlane

Locales: Firefox is available in many languages. For the official list, head over to the downloads page. For 1.0.x builds, you can get installable language packs (for Linux, Mac, and Windows). If you are not comfortable with starting in a different language from the command line, use the Locale-Switcher extension.


Migration: Firefox wants you to move over from other browsers, and it provides some tools to help you do so. If you are coming from Internet Explorer, there are some pages at Help -> For Internet Explorer Users to help ease the transition.


Nightlies: Want to try bleeding-edge builds with the latest bug fixes and features (at your own risk, of course)? Details on how to, with some commentary on builds, are over at the Burning Edge, or see Hack 92 (PDF).


Open source: Firefox is an open source project, having sprung from the loins of the Mozilla suite, now officially no longer supported by the Mozilla Foundation.

Overlays: Chunks of UI and implementation that you can add into Firefox to enhance the GUI or make it behave differently (Hack 87).


Password Manager: Where all your website login details are stored, if you choose to save passwords (this is on by default). You can access via Options (Privacy -> Saved Passwords).

Pop-ups: Firefox has one of the best pop-up blockers around, and is taking steps for the 1.1 release to handle the new breeds of pop-ups and pop-unders.

Portable: While not official builds, these versions have been optimized to run Firefox from a removable USB or CD drive. Ideal for bringing your installed extensions around with you. See Hack 31.

Profiles: Where the configuration and personal information is stored for a particular user of Firefox. You can manage users using the Profile Manager (ProfileManager, from the command shell).


Quirks mode: A Gecko rendering mode that is applied to content pages when the layout intent is not known or the content is not well formed (Hack 58).


Resource Description Framework (RDF): A data representation syntax that Firefox uses extensively under the covers in Bookmarks, History, and elsewhere. Extension authors can use RDF for many things, including XUL templates (Hack 70).

RSS: Firefox does RSS. See Livemarks.


Safe Mode: An escape route to open Firefox if it gets hosed and can't open. The most common cause of this is an extension that has not installed correctly or has bad code. In Safe Mode, you can uninstall or disable such extensions. You can start in Safe Mode from the command line with the -safe-mode switch, or if you're on Windows, there is an icon bundled with the Programs entries.

Searching: Firefox makes searching the web easier. There is the Search box with support for multiple engines, and Smart Keywords.

Smart Keywords: A mechanism to allow you to search from the location bar using shorthand terms. For example, "y vegetarian recipes" will look up Yahoo ("y") with the given search term. Learn how to create them over at the Smart Keywords feature page.

Support: Firefox is free to download, but this doesn't mean you can't get help if you need it. The best ways are via the Mozillazine forums or certain mailing lists. You also have the option of (rather expensive) email and phone support. All options are listed on the Mozilla support page.


Themes: Change the way Firefox looks with one of the wonderful themes available from Mozilla Update.

Tabbed browsing: We take it for granted now, not having our desktop cluttered with multiple windows. Mozilla was among the first to bring this feature into its browsers.


Update: Firefox periodically checks and will notify you of available updates to the browser and installed extensions. Enable this via Options (Advanced -> Software Update). Look for the icon in the top right of the menu bar--it will alert you if updates are available.

Figure 3
Figure 3. Software Update in progress


Validate: Firefox is a web developer's dream, providing excellent standards support, useful error messages and feedback, and a host of powerful developer-friendly extensions such as Live HTTP Headers and the Web Developer Toolbar.

Volunteers: Firefox would not be what it is today with the brilliant work of thousands of volunteers, contributing their time for coding, evangelizing, marketing, and many other tasks. You too can help (Hack 100).


Weather: Keep up to date with the latest forecasts with the ForecastFox extension.


XML: Firefox does XML well. It uses it internally, as well as rendering many different syntaxes in the browser (Chapter 6).

XP (a.k.a. Cross Platform): Use Firefox on multiple operating systems. The three main platforms where official builds are provided are Windows, Linux, and Mac OS X, but for each release you will find contributed builds for other platforms. Check the release notes for more details.

XPI: The install format for Firefox extensions, this is essentially a bunch of compressed files.

XUL (pronounced "zool"): Throw together a traditional user interface with the same speed that you throw together a web page. Mozilla's cutting-edge UI specification technology makes extensions and whole applications easy to create (Chapter 7).


Your browser: Firefox is your browser, so you decide how it looks, what buttons go where, and what you like and dislike, and then you get to tell the world about it.


Zzzzzzzzzzzzzzzs: Get some sleep now, knowing that you will be safe while browsing with Firefox. Security is good (Chapter 2), and the developers put enormous emphasis on dealing with this issue. Check Mozilla's Security Center and read how security bugs are handled for more details.

In March 2005, O'Reilly Media, Inc., released Firefox Hacks.

Brian King is an independent consultant who works with web and open source technologies.

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