Firefox 42 will be unveiled officially on November 3, 2015 by Mozilla. This guide walks you through the core changes and feature editions of Firefox 42 for the desktop and Android.

All other Firefox channels will receive updates as well on this date. In particular, this means that Firefox Beta will be updated to Firefox Beta 43, Firefox Developer Edition to version 44, Firefox Nightly to version 45, and Firefox ESR to version 38.4.

The information you find below covers only Firefox 42 and no version that is still in development. I suggest you check out our Firefox category here on Ghacks if you are interested in keeping an eye on future changes as we cover those regularly here.

Firefox 42 is a big update that brings along with it notable new features and the long awaited 64-bit version of the browser for Windows.

Firefox 42 download and update

If you are running Firefox already you may use the internal update checker to download and install the new version. Please note that updates may not yet be available depending on when you are reading this post.

To check for updates tap on the Alt-key on your keyboard, and select Help > About from the menu that opens up.

This displays the current version of the web browser and whether an update is available. If it is, it may either be downloaded and installed automatically or manually depending on the update settings of the browser.

If you are new or want to download an installer instead, use the following links to do just that.

Special Case: Firefox 32-bit to 64-bit

You cannot upgrade a 32-bit version of Firefox to 64-bit directly. What you need to do instead is download and install the 64-bit version, and have it use the Firefox profile that you are using in the 32-bit version so that you don't lose any data in the process.

I suggest that you create a backup of the profile before you do that though to be on the safe side.

How do you know if you are running a 64-bit version of Firefox? Load about:buildconfig in the browser's address bar and check the "target" string under build platform. If you see "64 in the string you are running a 64-bit version of the browser.

Firefox 42 Changes

The introduction of 64-bit stable builds are not the only important change in Firefox 42.

Private Browsing with Tracking Protection

Originally designed to come out with Firefox 39, Tracking Protection is finally launching in this version of the web browser.

It is an add-on for the browser's private browsing mode that blocks a selection of web trackers automatically in that mode.

To enable or disable it, load about:preferences#privacy in the browser's address bar and check or uncheck the "Use Tracking Protection in Private Windows" box on the Privacy page once it opens.

The effect? A comparison of the loading time of the top 200 Alexa websites came to the conclusion that load time dropped by 44% on average with Tracking Protection enabled. In addition, it reduced the average data usage by 39% and the number of HTTP cookies set on the system by 67.5%.

New Control Center with site security and privacy controls

A new shield icon is displayed under certain conditions in regular browsing and private browsing mode.

In regular mode, it will tell you if the connection to the site is secure or not. In private browsing mode, information about trackers found on the page and controls to disable the Tracking Protection feature are added.

Audio indicators and one-click audio muting

Audio indicators and muting options are finally available in all versions of Firefox. The browser indicates if audio is playing in any of the tabs open in it with an icon that it adds to the right side of the page title.

You may click on the icon to toggle the audio at any time to either mute the audio or unmute it. Please note that this won't affect playback of the media content on the page in any way though.

This can be very useful to indicate where audio is coming from, especially if it starts playing in the background, for instance when triggered by advertisement or an auto-playing video on a page.

Other changes

Improved performance on interactive websites that trigger a lot of restyles

Login Manager improvements: improvements to saving usernames and passwords, options to edit and show all logins in line, and migration of passwords from Chrome and Internet Explorer on Windows.

Media Source Extension support is available on all sites visited in the web browser.

WebRTC improvements: IPv6 support among other things.

Developer Changes

Firefox for Android

Most changes made to the Android version are identical to those of the desktop version. This is true for Tracking Protection in private browsing for example or under the hood improvements.

The changes listed below are exclusive to Firefox 42 for Android.

Android changes

External urls (for instance from chat applications or email apps), can be opened in the background now in Firefox for Android. Family friendly browsing supported when restricted profiles are created on tablets. Voice input for searching from the URL bar supported.

Security updates / fixes

Mozilla reveals security patches after the official release. We will update the review as soon as they become available.

2015-133 NSS and NSPR memory corruption issues

2015-132 Mixed content WebSocket policy bypass through workers

2015-131 Vulnerabilities found through code inspection

2015-130 JavaScript garbage collection crash with Java applet

2015-129 Certain escaped characters in host of Location-header are being treated as non-escaped

2015-128 Memory corruption in libjar through zip files

2015-127 CORS preflight is bypassed when non-standard Content-Type headers are received

2015-126 Crash when accessing HTML tables with accessibility tools on OS X

2015-125 XSS attack through intents on Firefox for Android

2015-124 Android intents can be used on Firefox for Android to open privileged files

2015-123 Buffer overflow during image interactions in canvas

2015-122 Trailing whitespace in IP address hostnames can bypass same-origin policy

2015-121 disabling scripts in Add-on SDK panels has no effect

2015-120 Reading sensitive profile files through local HTML file on Android

2015-119 Firefox for Android addressbar can be removed after fullscreen mode

2015-118 CSP bypass due to permissive Reader mode whitelist

2015-117 Information disclosure through NTLM authentication

2015-116 Miscellaneous memory safety hazards (rv:42.0 / rv:38.4)

MFSA 2015-115 Cross-origin restriction bypass using Fetch

Additional information / sources

Summary Article Name Firefox 42: Find out what is new Description A thorough look at the new features and changes in Mozilla's Firefox 42 Stable release. Author Martin Brinkmann

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