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Mozilla today launched Firefox 48 for Windows, Mac, Linux, and Android. The browser has gained multi-processor support (finally), enhanced protection against harmful downloads, and media improvements on Android. Support for old OS X versions and Android Gingerbread has been dropped.

Firefox 48 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 by far is the rollout of multi-process support. Mozilla has been building multi-process Firefox support for years as part of the Electrolysis project, and now it’s finally starting to roll it out.


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In fact, work to make the frontend and add-ons support multiple processes began in early 2013. Firefox Nightly gained multi-process support in November 2014.


In Firefox 48, Mozilla is slowly enabling multi-process support, starting with 1 percent of users, and ramping up to nearly half of the Firefox Release channel. To check if you’re in the Electrolysis group, type “about:support” into the URL bar and check to see if it says “1/1 (Enabled by default)” under the Multiprocess Windows line item.

Just like other browser vendors have concluded, Mozilla believes using a separate rendering process lays the foundation for significant performance and security improvements in Firefox. By separating web content and Firefox UI processes, when a webpage is consuming a large part of your computer’s processor and memory, your tabs, buttons, and menus (hopefully) won’t lock up.


Multi-processor support breaks some add-ons, especially those that modify content. As such, Mozilla will be testing multi-process support with add-ons starting in Firefox 49. The intent is to make it the default for all Firefox users in the first half of 2017. In the meantime, the company is asking add-on developers to check whether their add-on will likely be affected and to test it.

Speaking of add-ons, Firefox 48 also makes extension signing mandatory. Add-ons that have not been verified and signed by Mozilla will simply not load.

With the release of Firefox 40 in August 2015, Mozilla kicked off its plan to require that all Firefox add-ons are certified, regardless of where they are hosted. Digital signing will be done through

The main reason is security, Mozilla has previously explained:

We currently use a blocklisting mechanism to defend against malicious add-ons, but additional measures are needed to better protect our users as some add-on developers have adapted to work around blocklisting. Blocklisting is also reactive: users can be harmed by dangerous add-ons that are installed until they are identified and blocked.

In the same vein of security, Firefox 48 drops support for OS X 10.6 Snow Leopard, OS X 10.7 Lion, and OS X 10.8 Mountain Lion. If Apple hasn’t convinced you to upgrade your Mac, Mozilla is giving you a nudge.

Also in Firefox 48, WebExtensions are now considered stable. With mandatory signing and by moving to WebExtensions, Mozilla is hoping the review process for add-ons will be much faster.


Next up, Mozilla has tweaked the browser design to make “the awesome bar even more awesome.” When you enter a new query, you’ll see more suggestions than before (as shown above), a wider view of your suggestions across the screen, and icons when a suggestion is recommending a site that is already in your bookmarks or open tabs.


The Discovery Pane at about:addons has been redesigned with cleaner images and text. The goal is to simplify installation for featured add-ons to just one click.

Last but certainly not least, Firefox 48 includes security improvements that enhance download protection. This is based on Google’s Safe Browsing service, which provides lists of URLs that contain malware or phishing content to Chrome, Firefox, and Safari browsers, as well as to Internet Service Providers (ISPs).

Thanks to Google, Firefox 48 now has protection against two additional kinds of downloads: potentially unwanted software and uncommon downloads.

The former is for software that makes unexpected changes to your computer, collects your personal information without your consent, and uses techniques to make it difficult to uninstall. The latter covers downloads that may not be malicious or unwanted but that are simply not commonly downloaded, letting users know this may not be the download they think it is.

Mozilla has also tweaked Firefox’s user interface to make it easier for users to notice and understand warnings for these downloads:


There are also new options in Firefox’s settings for users who want to tweak these warnings:

  • Block dangerous and deceptive content: This enables warnings when visiting pages which contain malware or deceptive content. It is required by the rest of the Safe Browsing functionality.
  • Block dangerous downloads: This enables the download protection feature which may use a remote server to detect malicious executable files.
  • Warn me about unwanted and uncommon software: This extends the download protection feature to also warn about potentially unwanted and uncommon downloads.

Unless you know what you’re doing, you should probably leave all these on.

Here’s the full Firefox 48 changelog:

  • Roar for moar protection against harmful downloads! We’ve got your back
  • Process separation (e10s) is enabled for some of you. Like it? Let us know and we’ll roll it out to more.
  • Add-ons that have not been verified and signed by Mozilla will not load
  • GNU/Linux fans: Get better Canvas performance with speedy Skia support. Try saying that three times fast
  • WebRTC embetterments: Delay-agnostic AEC enabled, Full duplex for GNU/Linux enabled, ICE Restart & Update is supported, Cloning of MediaStream and MediaStreamTrack is now supported
  • Searching for something already in your bookmarks or open tabs? We added super smart icons to let you know
  • Windows folks: Tab (move buttons) and Shift+F10 (pop-up menus) now behave as they should in Firefox customization mode
  • The media parser has been redeveloped using the Rust programming language
  • Heyo, Jabra & Logitech C920 webcam users. We fixed those pesky WebRTC bugs causing frequency distortions. Buh-bye, squeaky voice!
  • Improved step debugging on last line of functions
  • So long to support for 10.6, 10.7 and 10.8. Now we can focus on where most Mac users are: 10.9. Don’t forget to upgrade!
  • After version 48, SSE2 CPU extensions are going to be required on Windows
  • Au revoir to Windows Remote Access Service modem Autodial
  • WebExtensions support is now considered as stable
  • Want to move absolute & fixed positioned elements? (Who doesn’t, right?) Now you can with our geometry editor.
  • The memory tool now has a tree map view for your debugging pleasure. It’s a little bit of “boo” and a whole lot of “ya.”
  • We’re putting the spotlight on the background. Now you can debug WebExtensions background content scripts and background pages
  • Content Security Policy (CSP) is now enforced for WebExtensions. (Who’s down with CSP?)
  • Old and busted: Error Console. New hotness: Browser Console for your debugging pleasure.
  • Add-on development just got easier because you can reload them from about:debugging — because we’re all about debugging.
  • This theme is hot, hot, hot! Say hi to the Firebug theme for Developer Tools.
  • Expand network requests from the console panel to view request details in line, so you can see things in context
  • Workers can now use the Web Crypto API

If you’re a web developer, more details are available for you here: Firefox 48 for developers.


Firefox for Android has a slew of minor but notable improvements. The biggest is improvements to audio and video playback.

Now when you are playing a video in Firefox for Android and receive a call, your device will pause the video automatically. There’s also a new toolbar so you can quickly manage your audio controls within the app, and the touch controls on all video content are streamlined. MediaRecorder on Android is now supported via software codecs, and Audible playback now works with the Android Audio Service.

Firefox for Android also merges your Reading Lists into Bookmarks and your Synced tabs into the History Panel. As a result, your reading list items will now be available across your devices where you have Firefox installed.

Firefox 48 drops support for Android Gingerbread (versions 2.3 through 2.3.7). To be clear, Firefox still works on Android Gingerbread devices, but they can’t upgrade past Firefox 48, which is the last version for the old Android version. Android Honeycomb support was dropped after the release of Firefox 45.

Here’s the full Firefox 48 for Android changelog:

  • Adding Qwant as a search option for French, United Kingdom English and German locales
  • Amazon product search suggestions added to Awesomescreen Search
  • New users will now have an entry point to sync from the History panel
  • Android media improvements: Record all the things! MediaRecorder on Android is now supported via software codecs
  • Better Audible playback FTW! Now with Android Audio Service.
  • Want Firefox as your default? Of course you do. So we made it easier.
  • Stay in the loop! Get and control notifications for websites of your choice.
  • Come here often? We let you add frequently-visited sites to your home screen
  • Android Marshmallow/6+ peeps: We added a sweet action bar that floats near your selected text. No more traveling to the top of the screen!
  • Mobile history comes before synced desktop history on your phone or tablet. Of course!
  • Reading List is now in your Bookmarks panel
  • Sync Tabs is now in the History panel
  • We restore your tabs by default. Don’t want that? You can change it in Advanced Settings. You’re in control
  • Support for Android 2.3 (Gingerbread) has ended. Farewell!
  • Video controls get a new look! Snazzy
  • WebExtensions support is now considered as stable
  • Deliver asynchronous notifications via Push API

Mozilla releases new Firefox versions every six to eight weeks, and Firefox 49 is currently slated for mid-September.

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