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Browser extensions extend your web browser with additional features, modify web pages, and integrate your browser with the other services you use. This guide will introduce you to the world of browser extensions and help you get started.

If you’re a geek, this stuff is obvious to you. We geeks take this for granted — we know exactly what browser extensions can do, when to use them, and what to avoid. But not everyone knows all this stuff.

Why Would You Want to Use Browser Extensions?

You might want to use a browser extension for a few different reasons:

  • To integrate with other services you use. For example, Evernote offers an extension that allows you to easily clip websites and save them to your Evernote account.
  • To add additional features to your browser. For example, the JoinTabs extension for Chrome gives you a button you can click to combine all your Chrome tabs from multiple windows into a single window.
  • To modify websites as they appear on your computer — adding, removing, or modifying content. For example, the InvisibleHand extension adds information to shopping websites, informing you if there’s a cheaper price available on a competing retailer’s website.

Extensions can do many other things. They’re like any other piece of software, although browsers place some limits on what they can do. If you want to integrate your browser with a service or get an additional feature, there’s a good chance you can do it with a browser extension that already exists.

How Secure Are They?

Browser extensions are like any other piece of software. Malicious extensions could do bad things and even well-intentioned extensions could have bugs. As with any other type of software, from Windows desktop apps to iPhone apps, you should try to pick trustworthy extensions.

Chrome gives you some idea of the permissions an extension requires when you install it, so you can see if the extension is only operating on a single website or has additional permissions. Firefox doesn’t have a fine-grained permissions system, so extensions have access to the entire browser — and more. Internet Explorer has limited support for add-ons.

You should be particularly careful with browser extensions. They’re running in your browser, so a bad extension could use its access to snoop on your browsing, possibly capturing your credit card numbers and passwords. However, while it’s good to bear this in mind, the actual risks — assuming you stick with extensions from well-known developers and well-reviewed extensions with lots of users — are fairly minimal.

Will They Slow Down Your Browser?

You shouldn’t overload your browser with extensions. Each extension is another piece of code running on your computer. Just as you wouldn’t install a pile of applications you never use and let them run in the background on Windows, you should try to limit the number of extensions you use.

On Chrome, many extensions run in their own process, adding another process to your system. Firefox runs all extensions in the same process, but many additional extensions can make Firefox even slower.

Performance concerns shouldn’t stop you from using a few extensions that will really enhance your browsing, but bear in mind you don’t want to use too many. Try to only install ones you’ll actually use — if you don’t use an extension, uninstall it from your browser to reduce clutter and speed things up.

Differences Between Browsers: Chrome, Firefox, Internet Explorer

Different browsers have different extension systems. Firefox has the most powerful one. Many people use Firefox because of this — Firefox makes many advanced extensions possible that wouldn’t be possible on other browsers. Because of its history, even extensions that would be possible in another browser may only be available for Firefox.

Chrome also has a thriving extension ecosystem and there’s probably also a Chrome extension for most everything you’d want to do. Chrome places more limits on its browser extensions so they can’t be quite as powerful as they are in Firefox, but these limits allow Chrome to present a permissions system and restrict extensions a bit more for security.

Internet Explorer has a very small add-on ecosystem. Few add-ons are available, and most of the Internet Explorer add-ons in actual use are probably browser toolbars like the terrible Ask toolbar that were foisted on users through bundling with other software. If you want add-ons, Internet Explorer is not the browser to use.

Safari and Opera also have extensions available, but their ecosystems are much smaller than Firefox’s and Chrome’s.

Extensions Aren’t the Same as Plug-ins

Note that extensions, or add-ons, aren’t the same as browser plug-ins. “Plug-ins” are things like Adobe Flash, Oracle Java, or Microsoft Silverlight. They allow websites to embed and render content — Flash movies, PDFs, or Java applets, for example — that are rendered with the plug-in. Plug-ins are a common target for attackers because websites can load them and exploit bugs in them, while extensions are different. Websites you visit can’t use your extensions to do anything. Essentially, extensions add features you can use, while plug-ins add features websites can use.

Where to Get Extensions

Chrome extensions are available from the Chrome Web Store, while Firefox extensions are available on Mozilla’s Add-ons site. Microsoft hosts an Internet Explorer Add-on Gallery website, but the selection is extremely limited. Other browsers have their own sites.

Smartphones and Tablets

Browser extensions haven’t made the jump to mobile devices. Whether it’s Safari on iOS, Chrome on Android, or Internet Explorer in Windows 8’s Modern environment, none of these browsers has support for extensions. You’re probably better off using a dedicated app for whatever you want to do on mobile devices.

There are some exceptions. For example, Firefox for Android has support for browser extensions — but they must be developed specifically for Firefox for Android, not the desktop version of Firefox. The Dolphin browser for Android supports its own extensions, too.

On an iPhone or iPad, there’s no browser that supports extensions — not even the iOS version of the Dolphin browser — thanks to Apple’s limitations on what apps can do.

Bookmarklets are similar to browser extensions. A bookmarklet is a special bookmark that runs JavaScript code when you click on it. For example, you could have a bookmarklet that sends the current web page to Evernote instead of using the Evernote browser extension. Bookmarklets don’t bog down your browser because they only run when you click them — they’re not running in the background. They generally work in every browser, too.

Image Credit: Mikeropology on Flickr (modified)

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Chris Hoffman is Editor-in-Chief of How-To Geek. He's written about technology for over a decade and was a PCWorld columnist for two years. Chris has written for The New York Times and Reader's Digest, been interviewed as a technology expert on TV stations like Miami's NBC 6, and had his work covered by news outlets like the BBC. Since 2011, Chris has written over 2,000 articles that have been read more than one billion times---and that's just here at How-To Geek.
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