Mozilla plans to release Firefox 41 Stable to the public on September 22, 2015. This article walks you through all important changes, features and everything else that is new.

Since the release process is streamlined, all other editions of Firefox will be updated as well on that day.

This means that the following versions will be released tomorrow: Firefox 41 Stable, Firefox 42 Beta, Firefox 43 Developer Edition, Firefox 44 Nightly and Firefox ESR 38.3.

The information below covers only Firefox Stable and no other edition of the web browser.

Firefox 41 download and update

All versions of Firefox are configured by default to check for updates regularly. If you have not modified that setting you should be notified about that new version soon.

If you don't want to wait, these checks don't happen in real-time, then you can run a manual check for updates as well.

The easiest way to do so is to tap on the Alt-key on the keyboard, and select Help > About Firefox from the menu that opens when you do.

If you prefer, you can download the newest versions of Firefox from their official download locations as well. Note that some may not have been updated yet at the time of writing. Mozilla usually does that around the time the official announcement of the release goes live.

Firefox 41 Changes

Mozilla wanted to introduce add-on signing enforcement in Firefox 41 initially but pushed this back so that it is now scheduled to arrive in Firefox 43 instead.

The browser.newtab.url preference has been removed

Mozilla removed the browser.newtab.url preference in Firefox 41 which allowed Firefox users to set a custom new tab page using it.

Firefox users who still want to modify the New Tab page url can do so by installing the New Tab Override for the browser which enables them to do that.

Instant Messaging support added to Firefox Hello

Firefox Hello, a built-in communications module that allows you to make free video and voice calls to others, supports direct messaging in an instant messenger like environment in Firefox 41.

Simply start or join a conversation as usual. You can then start typing messages and hit enter to send them to everyone else participating in the conversation.

Binary XPCOM components are not supported anymore except as part of the application

If you are using a Firefox add-on that relies on binary XPCOPM components, you will notice that it won't work anymore once you update the web browser to version 41.

According to Mozilla's Benjamin Smedberg, the move was necessary as these represented "signigicant compatibility and stability risks to Firefox users".

Memory overhead of AdBlock Plus has been greatly reduced

If you have AdBlock Plus installed in Firefox you may have noticed that it may cause spikes in memory usage under certain conditions.

The main issue was that AdBlock Plus injected its stylesheet (of blocked resources) into every iFrame loaded on a page. While that did not matter on sites that used none or only a few, it resulted in huge memory spikes on sites that used many.

Firefox memory usage jumped more than a Gigabyte in extreme cases on sites that make excessive use of iFrames.

We have talked about this before and suggest you check out the initial post on the matter for details.

The fix, which we have reviewed here, improves memory usage by enabling the sharing of CSS data. AdBlock Plus users should notice memory improvements across the board thanks to the changes that Mozilla made.

WebRTC now requires perfect forward secrecy

Perfect Forward Secrecy limits the damage that can be done with compromised keys.

This means that the compromise of one [session] cannot lead to the compromise of others, and also that there is not a single secret value which can lead to the compromise of multiple [sessions]

Head over to Mozilla Hacks for additional information on the implementation.

Improved image decoding with performance up to twice as fast on some devices especially while scrolling

The release notes don't link to a bug listing on Bugzilla or mention details. It is unclear if this is related to support for Async Pan Zoom in Firefox or something else.

We have reviewed the APZ integration previously and found it to improve scrolling and zooming in Firefox significantly.

Other changes

Ability to set a profile picture for your Firefox Account

SVG images can be used as favicons. [Bug 366324]

WARP was disabled on Windows 7 after memory bug on YouTube, Deezer and probably other sites was reported on Bugzilla. [Bug 1188831]

Smoother and more reliable CSS animations via asynchronous animations [Bug 706179]

The media.autoplay.enabled preference now also apply to untrusted HTMLMediaElement.play() invocations too, that is calls from non-users activated scripts. [Bug 659285]

Enhance IME support on Windows (Vista +) using TSF (Text Services Framework)

Improved box-shadow rendering performance

Developer Changes

You can now take screenshots of selected nodes using Firefox's built-in Web Developer Tools. This is done by right-clicking on the node in the developer area (which you open with F12).

The Web Developer Tools rules view has additional copy operations added to it.

A right-click on image declarations in the developer tools allows you to copy the image as a data url.

Implemented Cache API for querying named caches that are accessible Window, Worker, and ServiceWorker

The command "security csp" has been added to the Developer Toolbar. It displays information related to Content Security Policy of the current domain (Open with Shift-F2). The Firefox Developer Toolbar is might useful for non-Developer related actions as well.

CSS Font Loading API enabled by default, see W3.org for additional details.

MessageChannel and MessagePort API enabled by default

Firefox for Android

Android changes

Swipe-to-close tabs on tablets

Quickly search with different search providers from the search panel

Overlay to manually search and copy/paste login credentials from login manager when they're not auto-filled

Improved bookmark management with duplicate bookmark detection

Open Android applications from a web page via Intent URIs

User Agent now includes Android version

Experimental new "speed dial" home panel add-on API

Security updates / fixes

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

MFSA 2015-114 Information disclosure via the High Resolution Time API

MFSA 2015-113 Memory safety errors in libGLES in the ANGLE graphics library

MFSA 2015-112 Vulnerabilities found through code inspection

MFSA 2015-111 Errors in the handling of CORS preflight request headers

MFSA 2015-110 Dragging and dropping images exposes final URL after redirects

MFSA 2015-109 JavaScript immutable property enforcement can be bypassed

MFSA 2015-108 Scripted proxies can access inner window

MFSA 2015-107 Out-of-bounds read during 2D canvas display on Linux 16-bit color depth systems

MFSA 2015-106 Use-after-free while manipulating HTML media content

MFSA 2015-105 Buffer overflow while decoding WebM video

MFSA 2015-104 Use-after-free with shared workers and IndexedDB

MFSA 2015-103 URL spoofing in reader mode

MFSA 2015-102 Crash when using debugger with SavedStacks in JavaScript

MFSA 2015-101 Buffer overflow in libvpx while parsing vp9 format video

MFSA 2015-100 Arbitrary file manipulation by local user through Mozilla updater

MFSA 2015-99 Site attribute spoofing on Android by pasting URL with unknown scheme

MFSA 2015-98 Out of bounds read in QCMS library with ICC V4 profile attributes

MFSA 2015-97 Memory leak in mozTCPSocket to servers

MFSA 2015-96 Miscellaneous memory safety hazards (rv:41.0 / rv:38.3)

Additional information / sources

Summary Article Name Firefox 41: Find out what is new Description Find out what is new, changed and removed in Firefox 41, the latest stable version of the popular web browser. Author Martin Brinkmann

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