Mozilla today launched Firefox 43 for Windows, Mac, Linux, and Android. Notable additions to the browser include a 64-bit version for Windows (finally!), a new strict blocklist for the browser’s tracking protection feature, and tab audio indicators on Android.

Firefox 43 for the desktop is available for download now on, and all existing users should be able to upgrade to it automatically. As always, the Android version is trickling out slowly on Google Play.

Mozilla doesn’t break out the exact numbers for Firefox, though the company does say “half a billion people around the world” use the browser. In other words, it’s a major platform that web developers target — even in a world increasingly dominated by mobile apps.


The biggest highlight in this release is undoubtedly the launch of Firefox 64-bit for Windows. This new version works on Windows 7 and above, meaning it should work on about 80 percent of Windows computers. You can download Firefox 64-bit from this page.

So, what does a 64-bit version of Firefox offer for the user? If you have a 64-bit system, the short answer is: running larger applications, faster execution, and increased security.

A 32-bit browser is limited to 4GB of address space, and while this may be surprising to some, web applications are getting bigger and bigger to the point where this can actually be an obstacle. Browser-based games, for example, especially those with native-like gameplay, are often much larger than typical online apps mainly because they have high-quality assets that must be stored in memory for synchronous loading.

For example, here’s a game built with Epic Games’ Unreal Engine running in Firefox:


“For some of the largest of these apps, a 64-bit browser means the difference between whether or not a game will run,” Mozilla explained earlier this year. A 4GB address space isn’t the only limit worth keeping in mind: Heap sizes, for example, are recommended to be 512MB in a 32-bit browser, while they can go up to 2GB in a 64-bit version of Firefox.

As for execution time, Mozilla says 64-bit Firefox is faster because it can access new hardware registers and instructions. This significantly speeds up how quickly JavaScript code can run.

The increased address space also lets Firefox use hardware memory protection and improves the effectiveness of ASLR (address space layout randomization). The end result means it is harder for malicious web content to exploit the browser.

There is, however, a bit of a caveat. Firefox 64-bit for Windows has limited support for plugins. Certain sites that require plugins and work in Firefox 32-bit might not work in this 64-bit version.

But Mozilla doesn’t see this as a big problem, and says it is by design. After all, the company plans to drop support for NPAPI plugins in Firefox by the end of the year (though it will keep Flash around). Mozilla has just over a year to deliver on that promise.

A 64-bit Firefox for Mac OS X and Linux has been available for years, but on Windows the feature never made it past the Nightly channel. In November 2012, Mozilla quietly killed off 64-bit Firefox, only to reverse the decision a month later after massive backlash from users.

In November 2014, the company promised to ship Firefox 64-bit for Windows “soon.” In March, the company launched a 64-bit version of Firefox Developer Edition. Now a stable release is finally available.


Aside from 64-bit support, Firefox has also gained a new blocklist. Firefox 42 added tracking protection to the browser’s Private Browsing mode.

Firefox, as well as the Focus content blocker for iOS, uses a blocking list based on the tracking protection rules laid out by the antitracking startup Disconnect. Anyone can view that open source blocklist over on GitHub.

The default protection list in Firefox’s Private Browsing blocks many advertising, analytics, and social trackers. Just like in Focus, Firefox now allows you to choose a “strict” protection blocklist that blocks additional content trackers.

“The other content trackers category includes things like video, photo, and embeddable content that tracks users,” Nick Nguyen, Firefox’s vice president of product, told VentureBeat last week. “Turning this category on will block some video embeds and may even break some sites completely.”

In other words, this is for the very privacy-conscious user. The tradeoff is that some sites will simply not work properly, so use this “strict” list with caution.

Here’s the full Firefox 43 changelog:

If you’re a web developer, more details are available for you here: Firefox 43 for developers. You may also want to check out Firefox Developer Edition, which got a big update last month.


Firefox 43 for Android isn’t a major release by any stretch. That said, the Android app is still getting some notable improvements.

The biggest one is the addition of tab audio indicators in the tab list. Firefox 42 added tab audio indicators to the browser for Windows, Mac, and Linux. Now Android users can also see which tabs are producing sound.


To use the feature, tap the numbered tab icon at the top of the screen. You’ll see the list of open pages — those that have a speaker icon beside them are making noise.


You can then tap the page to open the tab and decide how you want to deal with it. Unlike on desktop, there’s no option to just mute the tab.

Here’s the full Firefox 43 for Android changelog:

Mozilla typically releases new Firefox versions every six weeks, and we thus expect Firefox 44 to arrive before the end of January.