A plug-in (also called an add-in, an add-on or an extension) is a relatively small program that "plugs into" and complements the capabilities of its related main application by performing a specific, useful function. There are literally thousands of plug-ins for the Firefox and IE (Internet Explorer) Web browsers. In fact, many plug-ins come in versions that are compatible with both browsers. But there are more plug-ins for Firefox, because The Mozilla Foundation made it easy to develop extensions for its open-source browser.

Plug-ins can be silly or serious. Some plug-ins, such as Shockwave, are used by nearly everyone on the Web, whereas others have very specialized audiences. But no matter whom you ask, he or she will always claim to have “the best” plug-ins. Here, in no particular order, are some of the most useful.



Shockwave, from Adobe Systems Inc., enables Web browsers to play multimedia animated files, including sound. Shockwave is widely used on the Web, especially in small animated games. It’s available for Firefox and IE.



Flash Player, also from Adobe Systems, is the successor to Shockwave in many respects. While the two multimedia formats serve similar purposes, their plug-ins are not compatible. Flash, too, is available for Firefox and IE.



Firefox Showcase, from Mozilla.org, levels the playing field between Firefox and IE 7. In IE 7, you can display thumbnails of all open windows and tabs; Firefox Showcase adds the same capability to Firefox. Once you install the plug-in, a new Showcase submenu appears on the browser's View menu. You can choose to show thumbnails of all tabs in the current window or in all open windows. There are many options for displaying and opening tabs and windows. Most people just use the plug-in’s default settings.



Adblock Plus is considered by many Web surfers to be a must-have plug-in. It maintains a database of URLs that serve pop-up and banner ads and blocks them. If you see a banner ad, right-click it, select “Block” and you’ll never see it again. Or, you can use wild-card characters to prevent any content from being served from a given Web site. The easiest way to keep up with the ever-changing ad servers is the Adblock Subscription service, which automatically downloads updated lists of ad servers to your PC (available for Firefox only).



IE View, by Paul Roub, is a simple plug-in for Firefox that opens your current page or a selected link in IE. Unfortunately, there are still Web pages designed to be viewed properly only in IE. If you must visit such a page regularly, there is an “Always View This Page in IE” option. IE Tab is a similar program that opens the selected page or URL in a new tab.



Google Toolbar, from Google, is a popular plug-in that provides a host of capabilities. The autofill feature can automatically fill in your name, address and other frequently requested information, and you can have multiple profiles for family members. Also included are a bookmark manager, a pop-up blocker, as well as a spell-checker, a thesaurus and a translator. Last but not least, it also performs Google searches and allows users to add other search engines.



PDF Download, by Denis Remondini and Nitro PDF Software, is a Firefox plug-in for handling PDF files. Sometimes you want to view a PDF in your browser, and other times you want to see it in a separate reader. At times, you may also want to download and save it. This plug-in offers all three options each time you click a link to a PDF file.



TableTools, by Mingyi Liu, is a great Firefox plug-in for financial or scientific Web sites. It lets you properly sort, filter and copy HTML table data in formats that can be pasted into Microsoft Word or Excel. It also lets you search columns for a particular string of text. The sort/filtering routines are “smart” in that they automatically detect the data format (date:time, numbers, currencies and so forth) and sort or filter accordingly. This is a very powerful tool for a sophisticated audience.



TinyUrl Creator, by Jeremy Gillick, takes unwieldy, multiline URLs and converts them into short ones (like http://www.tinyurl.com/example); when entered into a browser, the shortened URL then redirects to the desired site. This is very handy when printing a URL for someone or when sending a URL via an email message that breaks lines after 70 characters.



Video Download, by ibai, lets you save streaming videos from Google Video, YouTube and many other sites with just one click. The plug-in redirects the streaming video to the developer’s site, where it is converted into the Flash format and downloaded to your PC. You need a Flash player to view the videos, but many are available for free. Video Download comes in versions for Firefox and IE.



ChromaTabs, by Justin Dolske, is a simple plug-in for Firefox that color-codes the tabs you have open. All tabs that belong to a particular site will be the same color. When you surf away from that site, the tab changes color.



Google Browser Sync, from Google, is a plug-in for road warriors. If you frequently work on different computers, you will miss your Firefox personal settings, bookmarks, cookies, stored passwords and so forth. Using your Gmail account, this plug-in will securely transfer all of that precious information from one PC’s browser to another.



Session Manager, by Morac, is for creatures of habit. If you visit the same sites every morning, just open all of them in separate tabs. Now create a name for the session like “Morning News” and save it. Instead of opening all those tabs one after the other, you can just click the session name to open all at once. The plug-in is only compatible with Firefox, though incidentally, the browser's built-in Bookmark All Tabs feature accomplishes pretty much the same thing.



Gmail Manager, by Todd Long, puts a small mail icon in your Firefox status bar, with a number indicating how many new messages you have. Clicking on icon takes you to Gmail. If you mouse over the icon, it shows how many spam messages you have, how much space your mail consumes and a summary of your 10 most recent messages.