Firefox 31 released: Find out what is new

Martin Brinkmann
Jul 22, 2014
Updated • Sep 1, 2014

Mozilla will release updates for Firefox on all channels and platforms later today that increase the version of the browser by one.

This means that stable users of the browser will get updated to version 31 automatically, while beta, aurora and nightly users are moved to Firefox 32, 33 and 34 respectively.

The update has not been released at the time of writing, but several third-party download sites and Mozilla's official FTP server are already listing it.

It is however recommended to wait until the update is officially released by Mozilla as last minute changes may make the non-profit organization pull what you have downloaded.

You can find out which version of Firefox you are running by loading about:support in the browser. There you find the version value listed under Application Basics.

Check out our download guide for Firefox if you need assistance with that.

Executive Summary

Feature-wise, Firefox 31 is a minor update just like Firefox 30 was. Below are the most important changes in this release:

  • A search field has been added to the New Tab Page.
  • Several under the hood changes such as a new default certificate verifier or generational garbage collection.
  • Ogg and pdf files are handled by Firefox by default if no handler is specified on Windows.
  • Implementation of CSS3 variables and WebVTT.

Firefox 31 Changes

The browser.tabs.closeButtons preference has been removed

Firefox supported several placements for close buttons on the tab bar of the browser. The default setting displayed close buttons next to each tab but you could modify the browser.tabs.closeButtons preference to modify that so that the close button was only displayed on the active tab, at the end of the tab bar, or not at all.

This preference is no longer functional and Mozilla suggests to users to use add-ons instead to change the tab closing behavior.

If you have modified it in the past, you will notice that Firefox has modified it automatically to the default again (which is one close button for each tab).

Add-ons such as Classic Theme Restorer provide you with the means to change that behavior.

Additional information about the change are available here.

Search Field on New Tab Page

search new tab page

One of the few changes in Firefox 31 that users will notice. Mozilla has added a new search field to the browser's New Tab Page that is displayed directly above the thumbnail grid.

The default search engine of the browser is used for this, and searches conducted here are loaded in the same tab.

There is no built-in option to turn it off. The next best thing you can do is install an add-on such as New Tab Tools that comes without a search option.

New default certificate verifier

Mozilla has developed the new certificate verification library mozilla::pkix! which replaces NSS in Firefox 31.The new implementation offers several advantages over the old:

  1. The code is more maintainable as it has been reduced to less than 5000 lines of code compared to NSS' more than 81,000.
  2. The new code handles cross-signed certificates better.

Additional details about that decision can be found on the Mozilla Security blog. Mozilla did make changes to policies as well which you find listed here.

Generational Garbage Collection

This is another under the hood change that most users may not notice at all. The implementation improves performance of Firefox, at least in some benchmarks.

Compacting Garbage Collection is the next big project in this regard. Mozilla hopes that it will reduce memory use significantly when it lands.

Ogg and PDF files handling on Windows

ogg file playback firefox

If no program is associated with ogg or pdf files on Windows, Firefox will handle these types of files directly. Firefox will use its internal pdf reader and the HTML5 media player for ogg files if that is the case.

WebVTT implemented


WebVTT is a text-based format that can be used to display text tracks using the <text> element. Its primary use is the display of subtitles when <video> elements are loaded.

Instructions on how to use WebVTT have been posted on the Mozilla Developer website. You can check out a sample HTML5 video that uses WebVTT here.

Other changes

Developer changes

eyedropper tool

  • CSS3 Variables have been implemented. [MDN article on CSS variables]
  • Add-on Debugger is a new Developer Tool. [MDN article on the Add-on Debugger]
  • Canvas Debugger is a new Developer Tool. [Mozilla Hacks article on the Canvas Debugger]
  • New Array built-in: Array.prototype.fill() - The fill()method fills all the elements of an array from a start index to an end index with a static value. -  [MDN article on Array.prototype.fill()]
  • New Object built-in: Object.setPrototypeOf() - The Object.setPrototype() method sets the prototype (i.e., the internal [[Prototype]] property ) of a specified object to another object or null. -  [MDN article on Object.setPrototypeOf()]
  • CSP 1.1 nonce-source and hash-source enabled by default
  • Eyedropper tool added to color picker in Developer Tools. Launch it via Alt > Tools > Web Developer > Eyedropper. A right-click copies the value of the color to the clipboard. [MDN article on the Eyedropper tool]
  • Editable Box Model. When you are using the Inspector, the box model view is displayed as well. You can now edit values in the box model view directly to change it on the page you are on.
  • Code Editor improvements. You can use Sublime Text key bindings by assigning "sublime" to the devtools.editor.keymap setting in about:config.
  • Console Stack Traces.  [Mozilla Developer article]
  • Copy as cURL. This copies the network request to the clipboard using the cURL command.
  • Styled console logs. Starting in Firefox 31, you can use the "%c" format specifier to style console messages.
  • navigator.sendBeacon enabled by default. [MDN article].
  • Dialogs spawned from the onbeforeunload event no longer block access to the rest of the browser.

Unresolved issues

  • Slow shut downs lead to 'Firefox is already running' warning (see 966469 and 985655)
  • Mac OS X and Windows: Citrix Receiver no longer works. As a workaround, mark the plugin as Always Enable in the addon manager (1025627)
  • GNU/Linux and Windows XP: Google Maps Street View displays a black screen (1034593)
  • Mac OS X: cmd-L no longer opens a new window when no window is available (1008793)

Firefox 31 for Android

Existing Panels on about:home can now be reordered

A panel displays information when you open a new tab page or the about:home page in Firefox on Android.Default panels that Firefox ships with display the history, top sites, bookmarks, and the reading list.

While it was possible previously to enable or disable panels, there was not yet an option to reorder them. This has changed now:

  1. Tap on the menu icon in the top right corner of the screen and select Settings from it.
  2. Select Customize on the settings page and on the next page Home.
  3. Long-tap on any panel installed here and select change order from the context menu that is displayed when you remove your finger.
  4. You can then use the move up or move down option to change its location.

Other mobile changes

  • Pull-to-refresh on synced tabs page. [bug 850600]
  • Locales added: Assamese [as], Bengali [bn-IN], Gujarati [gu-IN], Hindi [hi-IN], Kannada [kn], Maithili [mai], Malayalam [ml], Marathi [mr], Oriya [or], Panjabi [pa-IN], Tamil [ta], Telugu [te]
  • Most features of the desktop version are integrated as well.

Security updates / fixes

The security updates are

  • MFSA 2014-66 IFRAME sandbox same-origin access through redirect
  • MFSA 2014-65 Certificate parsing broken by non-standard character encoding
  • MFSA 2014-64 Crash in Skia library when scaling high quality images
  • MFSA 2014-63 Use-after-free while when manipulating certificates in the trusted cache
  • MFSA 2014-62 Exploitable WebGL crash with Cesium JavaScript library
  • MFSA 2014-61 Use-after-free with FireOnStateChange event
  • MFSA 2014-60 Toolbar dialog customization event spoofing
  • MFSA 2014-59 Use-after-free in DirectWrite font handling
  • MFSA 2014-58 Use-after-free in Web Audio due to incorrect control message ordering
  • MFSA 2014-57 Buffer overflow during Web Audio buffering for playback
  • MFSA 2014-56 Miscellaneous memory safety hazards (rv:31.0 / rv:24.7)

Additional information / sources

Now Read: Firefox Release Schedule

Firefox 31 released: Find out what is new
Article Name
Firefox 31 released: Find out what is new
Find out what is new in Firefox 31, the latest stable version of the Firefox browser released on Tuesday 22, 2014.

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  1. Jonny said on August 1, 2014 at 11:42 pm

    Yes I already use palemoon, but both are older version of Firefox, missing some of the good stuff we now see in v33. An officially supported x64 would be my ideal solution. Which is why I was asking Martin if he knows.

  2. Erick said on July 25, 2014 at 7:02 pm

    If you are on Windows, you can use Waterfox:

  3. Jonny said on July 25, 2014 at 1:03 pm

    Hi Martin,

    Is there any news or movement on an officially supported x64 FireFox release yet.

  4. Isaac James Allotey said on July 25, 2014 at 9:24 am

    Nice one

  5. TheAslan said on July 25, 2014 at 3:34 am

    I didn’t know that you can change the firefox default search engine.

  6. T.J. said on July 25, 2014 at 2:55 am

    Mr. Brinkmann, you might want to do a post on how Firefox is sometimes updating to new versions of its browser without permission. This had never happened to me before, until Firefox 31. Despite “Never check for updates” being unchecked and the about:config settings below set to false,
    I caught Firefox updating, and I was not using the internet, meaning I did not have Firefox started/open. I also had to uninstall “Mozilla Maintenance Service” which I had always refused to install in the past. I think Firefox is moving to the dark side (or this is a very, very bad bug?).

    1. db said on August 3, 2014 at 6:44 pm

      Same thing here. I was running ff23 and when I wasn’t online ff was caught updating to 31. Strange thing about it, it wasn’t until I restarted my computer a few days later, that it changed to ff31. I had 1-click weather running in the status bar just above the task bar and ff31disabled it and wouldn’t let me enable it. also the status bar was gone. But, get this, last night I added on status-4-evar, submitted a not happy to ff, and when I woke up this morning, i now have 1-click weather in the status bar. Don’t ask me how, but, maybe it’s because I’m still using xp.

    2. Zsolt said on July 25, 2014 at 11:07 am

      Firefox updates sucked for a while. Update usually start if you view the about window no matter what…
      If you have the maintenance service installed you can’t even stop it from happening.

  7. Erick said on July 25, 2014 at 12:39 am

    The Firefox 32 Beta notes are out, with attention to the New HTTP caching (v2), that is enabled by default (

    Other notes:

  8. David said on July 24, 2014 at 3:08 am

    Appallingly bad from the get go. Had to go in and do a bunch of work just to get it to stop bringing up the “welcome” page and then to make it save preferences from day 1.

    FF USED to be a great browser-but with each update I have more and more issues with it-and have to fiddle with it more and more.
    FF has absolutely and completely LOST sight of the concept of “easy to use”, “user friendly” and “WEB BROWSER”. Whatever they’re turning into-it is far from being the best browser on the web. Chrome or Opera are preferable.

  9. guest said on July 23, 2014 at 6:34 pm

    This new Google search on the new tab page is absolutely appalling. It’s stretching all my icons out and just getting in the way. How can the Firefox devs in 2014 be adding crap features with no means of turning them off? Do I really have to install an addon to modify my new tabs page? Every addon I’ve used for this purpose in the past has made my new tabs page very laggy. Can’t deal with lag.

    1. Zsolt said on July 23, 2014 at 9:04 pm

      There are no icons on the newtab page. I guess you meant the miniatures. But it doesn’t really matter. You can’t see crap on them anyway.

  10. said on July 23, 2014 at 4:41 am

    Why would anyone need multiple close buttons on tabs?

    Wonderful new CSS variable. That will save a lot of work when changing site colors. I hope all of the browsers will support it.

    background-color: var(–main-bg-color);

    1. Zsolt said on July 23, 2014 at 1:55 pm

      “Why would anyone need multiple close buttons on tabs?”
      What? You didn’t read it right… One for each browser tab.

  11. Zsolt said on July 23, 2014 at 1:12 am

    It’s also the new ESR which in my opinion is significant.

    “If you have modified it in the past, you will notice that Firefox has modified it automatically to the default again (which is one close button for each tab).”
    I don’t know about this. I have a close button only on the active tab on nightly without ever changing such settings.

  12. Gregory said on July 22, 2014 at 9:56 pm

    Did anybody notice that Mozilla abandons development of Desktop version of Firefox?
    All is going about and only for Android – no Desktop OS. What a shame Android is just one of many mobile OS.
    It’s not good for normal people with normal PC / Desktops without annoying touchable mobile OS.

    See these Features/Release Tracking

    Firefox is dying I can’t find best alternative of good and old FF.

    1. Trebuchette said on July 23, 2014 at 1:14 am

      Pale Moon really is the bomb. I think Moon Child needs to get a separate addons store (or maybe get one going for all legit gecko forks?) to cut all ties to Mozilla. In fact, I think he’s working on that, but I haven’t been by the forum in a few weeks.

  13. onedeafeye said on July 22, 2014 at 7:12 pm
    I just installed it, and it works as advertised – no close buttons.

  14. FF User said on July 22, 2014 at 7:05 pm

    I am seriously disturbed by the new safe browsing remote look-up feature in Firefox 31. It apparently transmits the full URL of many downloaded files to Google for verification.

    The primary reason that I use, and recommend, Firefox is that it historically has respected my privacy. Apparently this is NOT the case any longer, despite all of the claims to the contrary ( ). If the Mozilla developers feel that sending my download history to Google is not a violation of my privacy, who knows what else it is transmitting to other servers.

    1. Aram said on July 22, 2014 at 8:39 pm

      Only local look-ups are turned on in FF 31. Remote look-ups are scheduled to be turned on in FF 32.

      You can to turn off this feature by doing one of the following:
      1) Turn off browser.safebrowsing.malware.enabled in about:config or in the Preferences > Security > “Block reported attack sites.” This disables all Safebrowsing malware protection, including the warning interstitial that appears when the user navigates to a malware site.
      2) Replace browser.safebrowsing.appRepURL in about:config with an empty string. This disables application reputation checks but leaves other Safebrowsing malware protection intact.

      1. Martin Brinkmann said on July 23, 2014 at 7:07 am


      2. Trebuchette said on July 23, 2014 at 1:03 am

        What Brinkmann said: source? (Erick: sorry didn’t see your post. Forgot to refresh!)

        I realized I’d have forgotten most of these little about:config changes (much less testing them on each version to ensure they still do their jobs) when I quit upgrading. I’d prefer to use an “unsafe” old browser than a Google-bought-and-paid-for ad serving one. By FF 32 users will be expected to do 50 little about:config changes, and probably ADD 15 add-ons to an already impressive list, just to get basic browser functionality back (not to mention a reasonable expectation of privacy that we’d already come to expect in FF28).

        So Google: Hell no! CLEARLY Mozilla has sold out to Google and is trying to destroy gecko so people will be forced to consider Chrome or IE (and yeah, I’ll take IE before Chrome, but thankfully there are other options than these).

        Oh, Brinkmann: you should write about how Google Plus now requires a “modern” browser to even log in. You have to use LATEST versions of one of four browsers: IE, Chrome, Firefox, and Safari. (Yes: not only is old FF versions out, but Opera’s out entirely. That goes for Linux and Mac users, too: updated versions of Chrome, FF, and/or Safari ONLY.) Can’t wait till that “feature” hits you tube.

        Mozilla can suck it.

      3. Martin Brinkmann said on July 23, 2014 at 7:11 am

        I can sign in with Opera just fine. Which version did you test?

      4. Erick said on July 22, 2014 at 11:25 pm

        It’s working OK for me.

        Changes are made to
        “browser.safebrowsing.enabled” (Boolean)
        “browser.safebrowsing.malware.enabled” (Boolean)

        My “browser.safebrowsing.appRepURL” are not affected, and default value of it is:
        (it’s a string)

      5. Martin Brinkmann said on July 22, 2014 at 10:46 pm

        Aram or FF User, do you have links to bugs or blog posts about this?

  15. Gary said on July 22, 2014 at 6:16 pm

    I’m a tech by trade and it has always amazed me when a proven product, all of a sudden, was “upgraded to New and Improved”. This usually required the user to preform all sorts of acrobatics just to get back to the “normal” baseline. When you put a product out into the market you have usually beta tested and taken the time to take care of all the loose ends prior to the ship date. Why are there so many upgrades to a product that was a great browser, with great addons and a stability that out classed Internet Explorer by quanta. Please take the time to get the code right the first time and please listen to your “loyal followers” instead of bravely going to worlds unknown. Thank you

  16. Jan said on July 22, 2014 at 1:24 pm

    The removing of the tab close preference is a total non-sense for me. Why ? Did it harm anyone to have the ability to change it and : 1)have more text of the title in tabs ; 2)not close a tab by error anymore ?
    And seriously, recommanding an add-on to get back such a tiny preference ?

    The “under the hood” changes seems fine, but these like the one noted above give me the feeling they try to destroy their browser… Sad.

  17. EuroScept1C said on July 22, 2014 at 12:19 pm

    Waitin’ for 32 beta 1. Finally some interesting things will be in this new version. New cache, D3D11 OMTC etc.

    1. Erick said on July 22, 2014 at 4:11 pm

      Where did you see that? I’m curious about that new Cache!

      1. Martin Brinkmann said on July 22, 2014 at 4:58 pm
  18. Niks said on July 22, 2014 at 12:10 pm

    Can you write an article about ” Firefox vs Chrome ” in use of technology . Today I read somewhere that Chrome still uses GDI for fonts that was released in 1985 while Firefox , IE use Directwrite which was released in 2009 along with Windows 7 . I believed Chrome was using advanced technology . I am now wondering what else are differences between Chrome and Firefox in terms of technology . I have read HowtoGeek’s article “Here’s Why Firefox is Still Years Behind Google Chrome” published in 2013 but I would like to know more and updated article .

    1. Dwight Stegall said on July 24, 2014 at 4:50 pm
    2. Skits said on July 22, 2014 at 6:56 pm

      Up until recently font rendering for non-default fonts in Chrome for Windows was absolutely embarrassing. Everything looked rough and awful, while Firefox looked beautiful. I think they’ve fixed the font rendering from looking that badly recently, but I can’t speak for the core technologies each browser implements.

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