ActiveX is the mechanism by which Internet Explorer loads other applications in the browser. Through ActiveX, IE loads Windows Media Player, Flash, Quicktime, and other applications that can read files embedded in web pages. ActiveX controls are activated when you click an item such as a .WMV file on a web page to download it for display in your Internet Explorer browser window.

• As a Microsoft product, ActiveX was specifically designed to work with Windows systems. ActiveX is not supported by Microsoft on other operating systems such as Mac or Linux.

Firefox and other browsers that work on multiple operating systems use the Netscape Plugin Application Programming Interface (NPAPI) system. NPAPI performs functions similar to those of ActiveX.

Note: Firefox does not officially support ActiveX. However, if you require ActiveX controls, this article provides some background information and resources on ActiveX functionality and Firefox.

Table Of Contents

• Background on ActiveX
• ActiveX in Firefox
• Uninstalling the ActiveX plugin on Windows

Background on ActiveX

ActiveX was designed to make seamless media playback through Internet Explorer easier. When you select media on a web page, Internet Explorer downloads the content and calls the appropriate ActiveX control, as requested by the web page, to load the playback application in the browser, potentially with little or no involvement, by you.

• Because this system is capable of automatically downloading new ActiveX controls without your involvement, it has been exploited by spyware, viruses, and other malicious software. Internet Explorer has improved ActiveX security in a number of ways, and many of the security loopholes have been closed in IE 7. However, it is still relatively easy to download and activate a malicious ActiveX control on your computer.

An ActiveX control is the equivalent of an NPAPI plugin. However, ActiveX and plugin technology have differences. While the potential effects of malicious content are similar, plugins inherently have better security features. Plugins have less control over the web page in which they are embedded and cannot be used in applications other than a web browser. ActiveX has broader use across a greater number of applications.

ActiveX in Firefox

Since ActiveX applies only to the Windows platform, it is unsuitable for Firefox which is available across multiple platforms. Currently, there is no mechanism by which you can use ActiveX controls in Firefox 2.0 or later.

Until recently, a third-party plugin provided ActiveX functionality for Firefox. The Mozilla ActiveX Plug-in provided partial ActiveX support for Firefox 1.5 and earlier versions. By default, these ActiveX plugins were configured to execute only the two Windows Media Player ActiveX controls, which enabled the playback of video content through the Windows controls. There is a configuration file that can be used to enable other ActiveX controls. For details, see Adam Lock's site.

The plugins for Netscape, Mozilla Suite, and Mozilla Firefox were created by Adam Lock and are maintained on his site, which has not been updates since 2005. These plugins do not work with Firefox 2.0 or later.

• For more information, see Adam Lock's Mozilla ActiveX Project.

Note: Installing a version of the ActiveX plugin that did not match your Firefox version could cause it to ignore its configuration and run any ActiveX control - a significant security risk.

Uninstalling the ActiveX plugin on Windows

If you already have the Mozilla ActiveX plugin installed in Firefox, uninstall it as follows:

1. From the menu at the top of the Firefox window, select File and then select the Exit menu item.
2. Open My Computer or Windows Explorer.
3. Delete the following files:
   • C:\Program Files\Mozilla Firefox\plugins\npmozax.dll
   • C:\Program Files\Mozilla Firefox\components\nsIMozAxPlugin.xpt
   • C:\Program Files\Mozilla Firefox\components\nsAxSecurityPolicy.js
   • C:\Program Files\Mozilla Firefox\defaults\pref\activex.js

Based on information from ActiveX (mozillaZine KB)