The ability to add features to browsers makes them the most powerful applications on your screen, but with so many to choose from, where do you start?

Too many and you'll slow down your system; not enough and you're wasting an opportunity. Here's our guide to the ones you can't afford to be without.

1. Greasemonkey

Greasemonkey runs user-written scripts to completely alter many of your favourite websites, giving them a new look, invisibly mashing up different services and adding brand new features.

Visit the website at www.userscripts.org to see what's possible. It's available for Chrome and Firefox, and is built into Opera as UserJS.

2. AdBlock Plus

Many of us are virtually immune to online ads by now, but if you get a site that goes just that little bit too far, AdBlock Plus is the best way to slap it into shape.

It strips out everything from pop-ups to embedded Flash animations, making your browsing fast, smooth and less likely to make you feel the urge to reach for a Pepsi, the cool, refreshing choice of the new generation. As a bonus, it'll also strip out any malware too.

3. CooIiris

This is not just a media browser, but it's an incredibly impressive one too. CoolIris creates 3D walls of content from your favourite social sites, which doesn't sound like much until you see it in action.

Finding that one photo or video is so much easier when you can see all the options stretching out into infinity. It works on your desktop files too, giving you a great way to read everything.

4. Feedly

An alternative way of reading Google Reader, now in Firefox and Chrome. Feedly reparses your RSS feeds into a magazine-style format, making it less effective as a dedicated research tool or if you have to read every last story, but much smoother if you just want to see what's going on right now.

An icon on your toolbar brings it straight up, and if you want to go back into full research mode, it's easy to return to regular Google Reader. Get it from www.feedly.com.

5. Web Developer Toolbar

As the name suggests, you won't need this one if you never play with HTML and CSS, but if you do, you can't afford to be without it.

Now for both Firefox and Chrome, it adds all the options you need to troubleshoot your designs, from highlighting individual elements to poking at the CSS directly. Get it from www.chrispederick.com.

6. NoScript

Scripting technologies have made the web a more powerful place, but they sometimes just get in the way. NoScript lets you switch them on and off per page, but because it uses a whitelist to decide when it kicks in, you never need to worry about a rogue page jumping on your back before you can block it. It's only available for Firefox at the moment.

7. DownThemAll

One for hardcore file junkies, this pulls every file from a web page at a click, saving you the effort of going to each link, clicking 'Save Target As', and pointing it to a directory.

It's for Firefox only at the moment, from here. Chrome has its own equivalents though, including Download Selection, Download All that does the same thing as DTA, and a range of assorted downloaders for specific sites.

8. FireFTP

A complete FTP client inside Firefox. It's not as good as something like Filezilla if you use FTP a lot, for either website management or downloading lots of files, but if it's only an occasional thing these days, it's great to have something like this on hand to handle the gruntwork.

It's for Firefox only, and available from here. The closest Chrome equivalent that's currently available is Chrome FTP, although that's considerably less polished at this point.

9. Instapaper

Not an extension, but a bookmark that should work on anything – although you can get plug-ins as well. Instapaper stores any long articles you find and don't have time to read.

Best of all, as it's a web service, there are viewers available for almost everything, including any web-enabled computer. Get it from www.instapaper.com.

10. All-In-One-Gestures

Gesture support has to be used to be fully appreciated. Opera pioneered it in web browsers, and when you're used to it, it's impossible to go back. Navigate, close windows and more with simple sweeps of the mouse and it becomes an almost subconscious act.

If this specific plug-in doesn't work, there are others, although Opera still has the edge in terms of fluidity due to its built-in support. Get it from here.

11. Delicious Bookmarks

Another bookmark-based extension, in both ways. Syncing bookmarks is fine, but if you're like us, you quickly end up with far too many to manage.

Delicious is the perfect way to sort, share and tag anything of interest online. You can see what other people have said about them as well, and import them into almost any web browser or other link collection.

12. StumbleUpon

On the other hand, if you're having trouble simply finding something good to read online, sit back and let StumbleUpon show you the way.

Tell it what you're interested in and it finds you a page that might qualify. You can also add your own favourite sites to the collection, bookmark any of interest for later use, and comment or read comments on sites from other users.

13. AutoProxy

Proxy servers are a godsend if you want to access content you're not sup… to keep your online life private. And nothing else. Because that would be Very Naughty.

AutoProxy lets you switch back and forth between identities with ease. You'll still have to track down the right proxy server for what you want to do, and you should be careful that you switch it off before doing anything crucial like online banking, just to be safe.

14. Evernote WebClipper

This is the ideal way of keeping snippets of interest, images or any other clippable content from around the web. With the free Evernote package, you get 40MB a month, which is plenty for web content, and you can access it from any machine or on the major mobile platforms.

An IE plug-in installs with the desktop client (not required, but very helpful for managing your note collection), with Firefox/Chrome plug-ins available separately. Get it from www.evernote.com.

15. FoxyTunes

Don't waste time switching away from the web just because a Justin Bieber song 'accidentally' found its way into your music library. With FoxyTunes, you can control almost every major music player from within your browser – which, despite the name, can also be IE. Sorry, no Chrome.

Media is one area where Firefox definitely still has the advantage, with Chrome's only real plug-ins being for online players and simple look-up checks of services like Spotify's library. Get it from www.foxytunes.com.

16. IE Tab

Not many of us use IE by choice, but sometimes there's no other option. IE Tab lets you open up a window in Firefox or Chrome, but using the IE rendering engine instead. It gives you all the benefits, and is easily closed afterwards.

Chrome extensions

17. Session Manager

Most of us need more than one website at a time. Session Manager helps you recover from crashes by bringing up complete sets of tabs. It's available now for Firefox and the Chrome browser.

18. PrintPDF

You can download web pages easily enough, but if you want to make sure you see them properly on another platform, PDFs are the answer. PrintPDF is a tool that exports them directly.

For Firefox, see here. Chrome users should go to here.

19. Karbon FLV Downloader

This is a great way to download FLV video files and MP3s embedded in web page code. For FLVs, you'll need a dedicated Flash player to watch them later on, at your leisure. You can download it from here.

20. Bit.ly

The most popular of the URLshortener tools out there, Bit.ly takes any link you give it and crunches it down into a more Twitter/instant message-friendly format.

For Firefox, go to here. For Chrome, you need to head over to here.

21. Remember The Milk

One of the best task managers around, integrating beautifully with Gmail and available on iPhone and Android. The Firefox and Chrome plug-ins connect it with Gmail too. See www.rememberthemilk.com to download it.

22. Chrome Reader

One of the most bizarre and annoying things we've noticed about Chrome is that Google makes it incredibly fiddly to subscribe to feeds. This simple but incredibly effective plug-in fixes that problem immediately. You can download it from here.

23. Unhide Passwords

Security is rather pointless when you're alone, and Unhide Passwords removes the starring-out so you can see what you're typing.

It's for Firefox only, but there's a Chrome equivalent available from here.

24. Copy Without Formatting

When you copy text from the internet, it retains its formatting when you paste it. This add-on sits in Chrome and gives you a shortcut that only spits out plain text. Find it here, or get the handy Firefox equivalent from here.

-------------------------------------------------------------------------------------------------------

First published in PC Plus Issue 300

Liked this? Then check out 10 really useful Chrome browser extensions

Sign up for TechRadar's free Weird Week in Tech newsletter
Get the oddest tech stories of the week, plus the most popular news and reviews delivered straight to your inbox. Sign up at http://www.techradar.com/register

Follow TechRadar on Twitter * Find us on Facebook