Disable targets for downloads
Web page authors often set their download links to use target="_blank", ensuring their page stays on screen when the download commences, but causing a new (blank) window to appear in Firefox and Mozilla. This extension eliminates the blank browser window that pops up onto the screen when you start a download of a binary file. The "disable targets for downloads" extension may not have the snappiest name, but does boast the very useful feature of preventing these windows from appearing for binary files. You can control the list of files that the extension will "de-target" through the extension's configuration dialog.
In contrast to Google Preview, AdBlock does not add information to Web pages, but removes it. With AdBlock installed you can block images, Flash animations, iframes, scripts, and other Web page elements based on their source address, either as a wildcard or a regular expression.
The power of this approach is obvious. AdBlock can strip ads out of Web content, saving you bandwidth and removing the annoyance of ads appearing midway through content. Since many ads are now served by ad-hosting companies, a few wildcard blocks can significantly reduce the number of ads that you see in the average Web page. AdBlock can also block malicious or inappropriate content, although the openness of the configuration makes this inappropriate for use as anything other than a tool for personal preferences in this respect.
Using AdBlock is simple. Right-click on an ad and select "AdBlock ..." from the context menu. In the dialog box that appears, you can opt to alter the address that will be blocked, introducing wildcards for example to block all content from a given server. Alternatively, click "AdBlock" in your Firefox status panel and select from the list of blockable elements. You can quickly build a comprehensive set of filters using this technique.
If you use this tool, be aware of a sensitive issue. Although you may feel that your enjoyment of some Web sites is marred by the presence of ads, these ads represent a revenue stream for the Web site. If you block ads, there are those who would assert you are not holding up your end of a "social contract" between yourself and the Web site that you are browsing.