Plug-In Definition | The Interactive Glossary

Plug-ins, which may also be called plugins, browser extensions, or add-ons, are computer programs designed to work alongside a web browser. Plugins are typically developed by independent software developers, and not by the developer of the browser.

All major browsers allow the use properly designed extensions. Microsoft Internet Explorer was the first to allow extensions and did so in 1999. Mozilla Firefox followed suit in 2004. In 2009, the Opera browser was opened up to extensions, and both Google Chrome and Apple Safari began to allow extensions in 2010.

In the past, plugins and extensions were used primarily to add multimedia capability to web browsers. However, plugins for modern browsers are much more diverse and offer a broad range of tools, games, utilities, and more.

Also See: Browser, How to Install a Plugin

Frequently Asked Questions

Are plugins safe?

Browser plugins have a tremendous amount of power over the browser. Since they tie directly into the browser code, they have the ability to take a look at your history, watch every interaction that takes place in the browser, and change the way your browser behaves. As a result, you need to be very careful when selecting and installing browser plugins.

Plugin developers range from large reputable companies to small agencies and individual programmers. In most cases, when extensions are originally developed, the intentions of the developer are good. However, when a small agency or individual programmer develops a plugin, and then doesn't have the time to keep up with bug fixes and updates, it is not unusual for adware companies to come knocking. If the original developer sells the plugin, the goal for the adware company is to then introduce adware into the plugin code through automatic updates. In this way, more than one honest plugin has been converted into an ad-injecting, history tracking, privacy breaching piece of malware.

Plugins are generally safe. However, be careful who's plugins you install, and if you start to see unexpected behavior, deactivate plugins one by one to see if one or more may be doing more than what the original developer advertised.

What types of things do plugins do?

In the past, plugins were designed to do one of two things: add multimedia capabilities to the browser or add an additional toolbar to the browser interface. Multimedia capabilities were provided by plugins such as Flash Player, RealPlayer, QuickTime, and Shockwave. Today, Flash is still used, but the other multimedia platforms have mostly gone away except for certain niche applications. Most of the toolbars added to web browsers were of marginal value. Some added search capability – a feature now included by default in all major browsers – and many were simply adware in disguise.

Modern browsers can be equipped with extensions that do a lot more than the toolbar and multimedia player plugins of the past. For example, one popular plugin can be used to check for and correct grammar errors as you type content into a web form. Another plugin can be used so that you have easy access to chatting and video calls over Google Hangouts anytime your browser is open. One plugin that is popular with business professionals allows you to see LinkedIn connection profile details in Gmail so that those details are visible while you are crafting a message. There are many plugins that can be used to take a variety of types of screenshots of the contents of the browser window.

No matter what irritation you are trying to fix, or feature you want to add on, it's probable that someone has already developed a plugin that does just what you're looking for.

What are the most common plugins?

Plugin popularity varies by browser. However, to give you a sense of the sort of plugins that are popular with web users, some of the most popular extensions in the Firefox Add-Ons store include:

• Adblock Plus: An ad-blocking application that targets intrusive ads, such as pop-ups, while allowing unobtrusive ads.
• Video DownloadHelper: At utility that you can use to download video from sites like YouTube.
• Firebug: A front-end developer toolkit that allows a user to edit HTML, CSS, and JavaScript live in the browser.