This year's release of Firefox 3.5 gave us a lot of reasons to like it, but its extensibility remains everyone's favorite feature. These add-ons and theme tools were the most popular in the year gone by.


This list is culled from a straight listing of the most popular posts that offered a Firefox extension for download in 2009. We're not including posts about configuring Firefox, or even our own hand-rolled Firefox add-on packs—even if they were pretty popular, too. Let's get to the good stuff.


Lifehacker's Firefox Add-On Packs It used to be a pain to hunt down your favorite extensions every time you reinstall Firefox.… Read more

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One of the greatest things about Firefox is that its development happens way out wide in the open. When the design workers start coming up with preliminary sketches of a new release, anyone can peek at them and even compile them into a theme, which does just what the headline suggests.





Windows Vista and 7 feature some fairly nice looking transparency effects, but if your primary browser doesn't use them, it can feel a bit disconnected. All-Glass Firefox v2 tweaks your browser to look just, well, proper in its fancy-pants surroundings.




You can speed up Firefox by cleaning up its fragmented database, and the Vacuum Places Improved 0.3 extension automates that admittedly pain-in-the-butt process.





Google Redesigned, a multi-site suite that trades Google's blue/white/minimal look for a darker, sleeker feel, kept improving its transformative powers this year, adding a host of improvements in its 3.0 release, and later releasing a new version with GReader Redesigned for the RSS hounds.





"I'm having SUCH a bad day—the cleaning lady TOTALLY left her Pine Sol smell all over my bed linens!" That, my friends, is why clever JavaScript tweakers created the Dislike extension.




Many of the pictures and illustrations you find across the web aren't in their original form—and many can be had at better, perhaps more wallpaper-worthy sizes. The TinEye extension makes it a simple right-click maneuver to search out similar copies of any image you come across.





Sometimes, great stuff has to be hosted on public download services, because the file—or the attention it's getting—is just too much for our meek little personal sites. And the download sites often make it as painful as possible to grab those files. SkipScreen acts as an automated intermediary, jumping through the necessary hoops and entering the key presses required.





This neat little extension, winner of the Extend Firefox 3.5 contest, utilizes lots of Firefox's built-in features, like geo-location and the extension framework, to offer wary laptop users a way to nuke their personal data, passwords, and history if necessary, track where their machine is logging on after a theft, and cull all kinds of data from the thief. FireFound is, in other words, a smart thing to install if your laptop ever leaves the home.




A lot of helpful stuff is tucked away in Firefox's about:config menus. Gui:config brings them into focus and offers a graphical way to manage them. As the How-To Geek puts it, it's amazing that this isn't something being considered for mainstream distribution in the browser.




(Windows only): Firefox is decently light with memory on startup, but extensions and plug-ins drag it down as you actually use it. Memory Fox monitors Firefox's memory use and, once it reaches your pre-set limit, whips it back into shape.





(Windows only): Well, the headline and picture kind of say it all about Daum Blue, but it's worth noting that beyond looks, it's also fairly customizable, and looks even better on Vista and Windows 7 systems.



Sure, kind of anathema for this site's stated mission, but giving your mind a break at work has real mental benefits, even if your boss doesn't think so.




If you're likely to do more at a web site than just simply bookmark it, UrlbarExt is like a Leatherman for your AwesomeBar. Head to a site's root, search the site on Google, and do much more from a small array of address bar buttons.




Another headline that pretty much says it all. We weren't a big fan of Xmarks' new "discovery" features, but its growing reach into Chrome and other browsers make the former Foxmarks' expansion a good thing.




Given the recent legal crackdown on BitTorrent-centered sites, magnet links (explained here) are increasingly popular. Magnetiser makes it easy to track down a working torrent link to grab the file you're looking for.





It must be mentioned that, beyond smooshing together Gmail, Google Calendar, and Google Reader into one neatly-arranged Gmail page, Integrated Gmail also customizes every niggling detail of those combined apps, making it worth the try-out, even if you think you like your Google spaces separated into different tabs.




Omnibar is one of the clever ways Firefox can make itself into a Google Chrome clone, and we love that kind of openness 'round here.




If you're always looking at online purchases and wondering if you could save more before pulling the trigger, Invisible Hand affirms your hunches for you, dropping down and showing lower prices wherever it can find them.




Mozilla's future-facing automation and shortcut engine, Ubiquity, continued to get awesome-r in 2009.




We dug the idea of permanent, favicon-only tabs when a helpful reader explained it to us, but the App Tabs extension took a multi-step process and made it far more simple.




Not seeing your favorite add-on released in 2009 here, or covered anywhere at Lifehacker? Can't believe your favorite app doesn't get more attention? Let's hear all about it in the comments.