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Mozilla today launched Firefox 50 for Windows, Mac, Linux, and Android. The new version, which was delayed by a week to improve startup times, also includes download protection for more executable file types and new keyboard shortcuts.

Firefox 50 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.


First up, Firefox 50 was supposed to launch on November 8 but was delayed to today after a developer discovered the browser’s SDK module system is “a performance disaster.” More specifically, addons were spending over four seconds in a specific function before doing any actual work. A few issues were behind the overall performance problem, and all were addressed to improve startup time.


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Next, Firefox now has download protection for many more executable file types on Windows, Mac, and Linux. At the same time, the browser will reject stylesheets, images, or scripts if their type does not match the context in which the file is loaded. This is a big security improvement; while MIME sniffing (scanning the content of a file to detect the actual format and handle it appropriately) increases the speed of the web experience for most users, it’s a vector for attackers to exploit.

Firefox 50 also adds two new keyboard shortcut options. You can now set a preference to have Ctrl+Tab cycle through tabs in recently used order (as opposed to just the order in which they were opened). Meanwhile, Ctrl+Alt+R (command+alt+r on Mac) opens the page in Reader Mode.

Here’s the full Firefox 50 changelog:

  • Playback video on more sites without plugins with WebM EME Support for Widevine on Windows and Mac
  • Improved performance for SDK extensions or extensions using the SDK module loader
  • Added download protection for a large number of executable file types on Windows, Mac, and Linux
  • Increased availability of WebGL to more than 98 percent of users on Windows 7 and newer
  • Added Guarani (gn) locale
  • Added option to Find in page that allows users to limit search to whole words only
  • Updates to keyboard shortcuts: Set a preference to have Ctrl+Tab cycle through tabs in recently used order and view a page in Reader Mode by using Ctrl+Alt+R (command+alt+r on Mac)
  • Various security fixes
  • Fixed rendering of dashed and dotted borders with rounded corners (border-radius)
  • Blocked versions of libavcodec older than 54.35.1
  • Added a built-in Emoji set for operating systems without native Emoji fonts (Windows 8.0 and lower and Linux)
  • Changes for web developers

If you’re a web developer, more details are available for you here: Firefox 50 for developers.


Firefox for Android isn’t getting much in this update.

Here’s the full Firefox 50 for Android changelog:

  • Added support for HLS videos via player overlay
  • Simplified the user interface by combining the Recent Tabs and History panels

Mozilla releases new Firefox versions every six to eight weeks, but given the holiday season, Firefox 51 is currently slated for late January.

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