clear many kinds of private information quickly. The Settings button at the bottom of the Privacy tab opens the Clear Private Data settings window, where you can configure which kinds of information are cleared, and whether or not a confirmation window is shown, each time you use the Clear Private Data feature. From the settings window, you can also instruct Firefox to clear the specified information automatically each time it shuts down. See Chapter 14 for more information. The Content category The Content category (see Figure 16-5) configures the display of Web sites themselves. Figure 16-5: You can customize fonts and colors, turn off images, and configure sites through the Content settings. Popup Blocking Firefox blocks Web sites from opening popup windows without your consent, as I discuss in Chapter 9. To turn off popup blocking, deselect the Block Popup Windows check box. To allow popups on certain Web sites, click the Allowed Sites button to open the exceptions list. Some sites use popup windows legitimately and might not work properly without them. See Chapter 9 for more information about this feature. Extension and Theme Installation As I discuss in Chapters 17 (for themes) and 20 (for extensions), only the official Firefox site is allowed to install extensions and themes by default. When you try to install an extension or theme from another Web site, Firefox displays a warning toolbar that you need to dismiss before the installation can proceed, as I discuss in those chapters. To enable installation from certain trusted Web sites without a warning, leave the Warn Me When Web Sites Try to Install Extensions or Themes check box selected, and click the Exceptions button to open the Exceptions window, where you can specify a list of Web sites you trust. When you try to install an extension or theme from one of these sites, Firefox allows the installation without requiring you to deal with the warning toolbar. When you add a site to the exceptions list, the change takes effect immediately. Although clicking Cancel in the main Options window doesn't undo it, you can return to the list and use the Remove buttons if necessary. To enable installation from all sites, deselect the Warn Me When Web Sites Try to Install Extensions or Themes check box. Make sure you trust the company or individual offering an extension before you install it because malicious extensions could carry viruses or have undesirable side effects. Loading Images By default, of course, Firefox loads images on all Web sites you visit. To speed browsing or cut down on visual distraction, you can set Firefox to load only certain images or you can turn off images entirely. See Chapter 19 for more information. To prevent Web sites from loading images from other Web sites, select the For the Originating Web Site Only check box. This is a reasonable way to block advertising, but it can also break many pages, so I don't recommend it. For a better way to block ads, see the section on the AdBlock extension in Chapter 22. To turn off Web site images, deselect the Load Images check box. To block or allow images on certain Web sites, click the Exceptions button to open the exceptions list. If you keep images on, you can use this list to block certain Web sites from loading images. Likewise, if you turn images off, you can allow certain Web sites to keep loading them. To add a Web site to the list, simply enter its address (for example, http://www.ebay.com) and click the Allow or Block button depending on whether the site should be allowed to display images. This is a highly advanced feature. If you just want to block advertisements, see the section on the AdBlock extension in Chapter 22.