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Computerworld lists the top 10 Firefox extensions to avoid, based on whether they have any side effects, are memory hogs, or affect your browsing experience negatively. Check them out and comment on if you agree or not.

Fasterfox: This Web accelerator has a "pre-fetching" mechanism that makes you a very bad Web citizen. Here's how it works: You land on a page and start reading it. While your system is idle, Fasterfox silently starts following links and downloading the destination pages. The idea is that if you then decide to click on one of these links, the page is already cached on your local machine and will pop up very quickly.

NoScript : This extension is hugely popular and works as advertised, giving you control over which JavaScript, Java and other executable content on a page can run, depending on that content's source domain. You whitelist the sites you consider safe and blacklist the sites you don't.

Adblock and Adblock Plus : Obviously, we have some bias when it comes to ad-blocking extensions, as Computerworld is an ad-supported site. We also understand that these are very popular extensions. But if everyone blocked ads, how would sites such as ours continue to offer content free of charge?

PDF Download: Here's another extension that works as advertised and is very popular, but it seems like overkill for most users and can cause headaches for others. PDF Download lets you control how Firefox handles PDF files when you click on them -- you can display a pop-up box that lets you choose whether to download, open
or view the file as HTML. You can also set it to take one of these actions by default, skipping the pop-up.

VideoDownloader: Homegrown video is hot right now, and why not? Sites like YouTube and Google Video make it easy to put content online for Web denizens to enjoy. The VideoDownloader extension promises a way to download video from these sites and many more for your offline viewing pleasure. Sounds great, right?
The problem is that the extension has to connect to a Web site in order to work, and more often than not, you'll find that instead of a download window, what you get is "Service Temporarily Unavailable." When it does finally work, the download is
infuriatingly slow.

Greasemonkey: Hey, wait just a minute. Wasn't this on our list of best extensions? Well, yes it was. Greasemonkey is a really nifty extension to use, as long as you know what you're doing with it. It can potentially get you in trouble because it allows JavaScripts written by other people to run in Firefox. If one of those scripts is malicious, your system could be at risk. ScribeFire (formerly Performancing): This falls into the category of extensions that seem pointless. What we have here is a browser-based tool for writing blog posts. But don't most blogs already have a browser-based editor that works just fine?

TrackMeNot: This is another of those extensions for the overly paranoid. The developers apparently became concerned with search engine profiling -- the process in which search engines track your queries and build a demographic profile of you based on those queries -- after a list of three months' worth of search queries from 657,000 AOL members was released on the Web. A small section of a log file of searches performed by TrackMeNot. We don't mean to downplay privacy concerns, but the technique used in TrackMeNot is questionable. The extension runs in the
background while you surf, and sends random search queries to AOL, Yahoo, Google
and MSN search engines. What a waste of system resources for both you and the
search engines you rely on!

Tabbrowser Preferences: This extension lets you tweak Firefox's tab settings in various minor ways. For instance, you can add a New Tab button to your tab bar, or control whether the Close Tab icon appears on each tab or at the end of the tab bar. It works fine.

Tabbrowser Extensions: This extension is a real heavyweight but seems quite popular in certain Firefox circles -- it almost seems to be a rite of passage for Firefox nerds. It gives you lots of control over how tabbed browsing works and even supports plug-ins to add even more functionality. However, it is buggy and conflicts with many other extensions. In fact, even its developers suggest that you not install it!

Bonus: Watch out for the Numbered Links 0.9 imposter: There's nothing wrong with the Numbered Links 0.9 extension per se. By showing numbers next to links, buttons and other interactive elements on Web pages, it lets you navigate without using a mouse. If you chose to install Numbered Links 0.9 previously, there's no reason not to go on using it if you find it helpful (though you might be interested in Conkeror by the same developer).
However, if you see this extension in your add-ons list and don't recall installing it, then tread carefully. There's a version that has been modified into the FormSpy Trojan, which installs itself as a Firefox extension and keeps the title "Numbered Links 0.9." FormSpy can potentially capture information entered into HTML forms and send them on to a malicious Web site. For more information, see McAfee's FormSpy profile.