Firefox 15 clamps down on memory leaks

The latest update to Firefox brings a massive improvement to add-on and long browsing-session memory management, resulting in a much more stable browser.

Please note that the First Look video below is still applicable to Firefox 15, as is this Firefox How To collection, even though it features Firefox 4. A new video will be posted soon.

Firefox reborn in version 4


As you can see, Firefox is on version 15 at the time of this review. As a point of comparison, Chrome is currently on version 21 even though it only launched in 2008. The benefit, of course, is a browser that is safer and sleeker, with fewer problems because bugs get fixed on a regular basis.

The Firefox that you can download now is in the same speed category as its competition; offers many similar features (stronger in some areas and slightly weaker in others); includes broad, cross-platform support for hardware acceleration and other "future Web" tech and standards; and is a must-have for Android users (download for Android).

Firefox 15's big claim to fame is locking down memory leaks caused by add-ons, long browsing sessions, and heavy tab usage. The company released data showing huge gains in recovering memory with 150 tabs open, so you're likely to see big gains with only 50 tabs.

On the performance side, Firefox 15 now has Google's SPDY protocol on by default. That means that Web sites that support it, such as and, will load faster and safer. SPDY is safer because it forces SSL encryption for all connections.


Firefox installs quickly, your connection and hardware notwithstanding. There are no pop-ups asking you to register, and although an infobar link to Mozilla's Know your rights page at about:rights does appear, it's unobtrusive.

We're big fans of Firefox's rapid-release cycle. Initially wonky implementation has given way to a mature automatic update process. If you're on Windows, you'll be asked to agree to the User Account Control only when you install for the first time. Thereafter, the browser updates silently.

If you're installing Firefox for the first time, or installing after wiping all profile data, the browser will open to the new about:home Start page. It hosts a Google search box in the middle, and links to Downloads, Bookmarks, History, Add-ons, Sync, Settings, and Restore previous session at the bottom.

If you're updating Firefox from an older version, it checks your add-ons to see which ones you installed and which ones come from third-party vendors, such as security suite makers. The browser will ask if you'd like to disable any of these third-party add-ons. On top of that, all third-party add-ons are blocked from autoinstalling. Instead, you'll be presented with the option to allow them or block them on a per-case basis. This puts Firefox squarely on the side of the user.

We recommend that you set up Sync at this point, because it will allow you to synchronize and backup all your settings, add-ons, and personal browsing data. If you're extremely concerned about your data, you can set up Sync to work with your own server.


Note that people coming to Firefox from version 3.6 or older ought to be prepared for a lengthier install time because of the significant code changes since then.


As PCs continue to be rocked by mobile devices, many traditional desktop programs have found minimizing interface chrome to be popular. Google's Chrome browser kicked off this trend in a big way, allowing Web sites to shine through, and while other browser vendors have done their best to go minimal differently, it's hard to not acknowledge the lineage.

Firefox does a good job of taking the concept of minimal and putting its own spin on it. It has small navigation buttons the same height as the location and search bars. The Home button has moved to the right side of the location bar. Tabs are on top for heightened visibility and maximize space given to the Web site you're viewing, while on Windows the control menus are hidden behind the orange Firefox button in the upper left corner.

Menu options have been spread across two columns, and while nearly all the submenus have been redesigned, the hot keys remain the same for a gentle learning curve. In fact, the menu redesign makes it much easier to get to bookmarks, add-ons, and history, as they now all live on one Menu pane. The Menu button is not available to Mac users, to keep with the Mac OS X theme.



Right of the location bar lives the traditional search box, with its drop-down list of search engines. Above that on the tab bar there is a new button that lists all your open tabs, and you can add a button to access the Panorama tab-grouping feature. If you don't see the button, you can add it by right-clicking on the interface and choosing Customize, then dragging and dropping the Tab Groups icon next to the List All Tabs button. We don't consider many customizations to be essential, but this one is. The combination of tab grouping and Firefox's robust tab-memory management means you can keep open tabs around much longer than other browsers.



Features and support
Firefox is one of the most progressive major browsers available, an early adopter if not always an innovator. Its features cover the range of browsing essentials, from allowing you to heavily customize your browser while respecting your privacy, to giving developers the tools they need, to supporting the technologies that are driving the future of the Web.

One of the most important features in the modern Firefox is Sync. Sync smoothly synchronizes your add-ons, bookmarks, passwords, preferences, history, and tabs, not only with Firefox on other computers, but also with your Android version of Firefox. It's easy to set up, and if you're concerned about privacy, you can change sync to work with your personal server instead of Mozilla's. Firefox encrypts your data before sending it over an encrypted connection to its servers, where it remains encrypted. Mozilla says that the company would not be able to access it even if somebody there wanted to.

Tabs are a big part of browsing, and Firefox has the best tab management around. Thanks to recent memory-management improvements, you can now comfortably scale from two or three tabs to more than 100 without seeing a major performance hit over time. The aforementioned Panorama lets you group them out of sight until needed, and when you restart Firefox only the last open tab will become active. The others, while visible, won't load their content until you click on them. Panorama's groups let you label them which keeps organizational problems to a minimum.

The overall idea is to make it easier to switch from one tab to another, to group or regroup related tabs, and to get a global view of what's going on with your tabs. It's potentially a big improvement in browser usage, compared to aiming a mouse at a skinny tab, cycling through a list with Ctrl-Tab keystrokes, or pecking at a drop-down menu to reach the tabs that overflowed off into the deep.

Switch to Tab is a minor feature but incredibly useful. Open a new tab and start typing the name of an already-open tab, and the URL will appear in the drop-down with Switch to Tab beneath it. Select that one, and the new tab closes and you're whisked to the pre-existing tab. It's a great trick for cutting down on the amount of time it takes to sift through 45 open tabs, and removes the chance of accidentally having the same tab open twice or more.

You can also drag tabs around to reorder them, pin them as permanent "app tabs" next to the Menu button, or rip them off into their own windows.

Firefox add-ons have long been the brightest feathers in the browser's cap. While there are other more important browsing developments going on to close observers, add-ons remain important to the vast majority of people. The most popular Firefox add-ons have millions of users. The browser supports modern restartless add-ons, which install without needing to reboot the browser, as well as the legacy add-ons that helped drive its growth.

The add-on manager lets you search for add-ons without going to the external Mozilla Add-on Web site. You can create collections of add-ons to share in the Get Add-ons tab, navigate backward and forward through add-on searches, and as mentioned in the Installation section, it blocks add-ons from installing without your approval.

The Bookmarks and History menus, and Download Manager, leave a bit to be desired. They're not bad, but it's clear that they could use some redesigning when compared to the competition. We'd like to see them appear in their own tabs, as they do in Chrome, instead of in separate pop-up windows.

The location bar -- or as Mozilla calls it, the Awesome Bar -- retains familiar features, such as the options to search your history and bookmarks and to tap into your default search engine to provide you with quick results, without having to use the search box.

The "identity block," the colored left-most section of the URL, has been given a refresh to better call out the Web site you're on. The URL bar itself now changes the text color of the URL you're on so that the domain is black, for easy identification, while the rest of the URL is gray. This sounds small but is important, since it's a strong visual cue to help you avoid getting spoofed.

Also on the security front, Firefox was an early adopter of Do Not Track, which indicates via a header notification that you want to opt out of targeted advertisements. However, it requires that the Web site you're viewing, and therefore that site's developers, respect the header itself. While this is great for future-proofing the Web, not many Web sites have taken notice of it. That doesn't mean it won't eventually have a big impact, but that time is not now, and it's better to install an add-on like Adblock Plus or Do Not Track Plus to get more complete ad-tracking protection.



Under the hood, Firefox supports full hardware acceleration across all platforms, which means that the browser draws on your graphics card to speed up complex rendering. You'll see dramatic HTML5 support, including for high-definition WebM video, and broad support for the HTML5 canvas, video, audio, geolocation, drag and drop, and form tags. OpenType fonts are supported, as are CSS3 and newer JavaScript values. WebGL and hardware acceleration give the browser a massive boost, which we'll discuss in the Performance section below.

A new Web Developer menu collates tools for building and debugging Web sites in one location. One such is the ScratchPad tool, which browsers like Opera and Chrome have had for some time. It allows developers to test JavaScript and CSS before implementing it. The Web console feature also has a new autocomplete option and can have its location customized. Another dev tool, unique to Firefox, is a 3D visualizer called Tilt, that lets developers see in real time how their code will render on the site.


Firefox 15 introduces a series of memory-management improvements that dramatically increase the stability of the browser. These changes, covered by the internal Mozilla moniker MemShrink, basically mean that the browser can handle a huge number of tabs and add-ons longer than before. Firefox 15 is eminently stable.

As mentioned earlier, the browser's overall performance has been greatly improved by tying performance to the graphics processing unit (GPU) hardware acceleration. This allows the browser to shove certain rendering tasks onto the computer's graphics card, freeing up CPU resources while making page rendering and animations load faster. The tasks include composition support, rendering support, and desktop compositing.


CNET Labs will have an update to our performance benchmarks in the coming weeks. For now, our most recent numbers are from March 2011, when Firefox 4 was released.




Firefox has plug-in crash protection, which prevents plug-ins like Adobe Flash, Apple QuickTime, and Microsoft Silverlight from causing the browser to drop dead. If one of them crashes, simply reload the page.

Firefox is in an unusual position as the modern Internet stands on the precipice of the second phase of the digital age. As the world prepares for high-powered, always-connected smartphones to dominate, one of the most competitive and forward-thinking browsers comes from an independent nonprofit company.

Firefox's open-source approach and recent developer tools improvements means that the people designing your favorite sites will come back for more, while Mozilla's investment in pushing open Web standards means that the Web has a powerful, noncorporate advocate. Despite the heavy competition from Google, Microsoft, and Apple, and as long as it avoids stagnating, Firefox will have a bright future ahead of it.

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