Mozilla planned to release Firefox 39 on Tuesday but a last minute bug in the application required fixing so that the release has been delayed for later this week. In case you are wondering what this is all about, you find information about the malware-related issue on Bugzilla.

This is one of the cases where you may run into issues when you are downloading builds of Firefox from third-party download sites as you would have downloaded the version with the bug.

After working on the bug for several days, the organization pushed the final version of Firefox 39 to the official ftp server. It usually takes another day or two before the release is announced officially by Mozilla and then distributed to machines running Firefox provided that the browser is configured to update automatically to new versions.

Mozilla pushes out updates for all Firefox channels. This means that Firefox Beta will be upgrade to version 40, Firefox Dev to version 41, and Firefox nightly to version 42 of the browser.

Firefox ESR versions will be upgraded to version 38.1.

The following information provide you with detailed information about the Firefox 39 release.

Firefox 64-bit for Windows is a no-show again. Mozilla has not yet made a decision when it gets released other than stating that it will be in 2015.

Firefox 39 download and update

Firefox is configured to update automatically to new versions. While you can block this from happening, most users will receive update notifications once Mozilla releases the new version officially.

You may check for updates manually at any time with a tap on the Alt-key and the selection of Help > About Firefox from the menu bar a the top.

This opens a small window listing that performs a check for a new version. If it is found, it will be downloaded automatically to the system.

Direct downloads are provided as well if you prefer those. The links below lead to those so that you can download them and run the installer locally afterwards.

Firefox 39 Changes

The release is rather uneventful in terms of new major features or changes.

SafeBrowsing malware detection lookups enabled for downloads (Mac OS X and Linux)

This has been enabled on Windows machines for some time. It uses Google SafeBrowsing information to detect if downloads are malicious.

While it protects users from downloading malicious files, it has blocked legitimate files in the past as well.

Linux and Mac users not interested in Safe Browsing can use these instructions to disable the feature.

Share Hello URLs with social networks

If you are using Firefox Hello, a real-time chat component that Mozilla built-into Firefox, you know that you have several options to invite others to chat with you.

Mozilla added options to use the Share panel to share these links on social networking sites. It is not really that much of an improvement considering that you had options already to copy links to paste them on social networking sites you are using.

Asynchronous Plugin Initialization

Update: has not landed in Firefox 39 after all.

This is probably the most interesting feature addition for most users. Four of the top 10 chrome hangs in Firefox are related to plugin initialization and instantiation. The top chrome hang happens when plugin-container.exe child processes are created.

The patch modifies the old process by running most of the steps asynchronously. What this means is less wait time (for a step to complete) and thus less hangs as a consequence.

Additional information are provided when you load Bug 998863.

Reserved browser operations in multiprocess Firefox

Web pages may no longer prevent certain keyboard shortcuts in Firefox if it is running in multiprocess mode. The following commands are protected by the browser:

New Tab, Close Tab, Next and Prev Tab

New Window, Close Windows

Quit

New Private Browsing Window

Other changes

Removed support for insecure SSLv3 for network communications

Disable use of RC4 except for temporarily whitelisted hosts

The malware detection service for downloads now covers common Mac file types (Bug 1138721)

Performance of displaying dashed lines is improved (Mac OS X)(Bug 1123019)

Project Silk: Smoother animation and scrolling (Mac OS X) - Additional information here.

Support for new Unicode 8.0 skin tone emoi

Developer Changes

Support for 'switch' role in ARIA 1.1 (web accessibility) - click here for ARIA (Accessible Rich Internet Applications) information.

WebIDE now supports debugging Firefox OS devices over Wi-Fi (instructions)

Drag and drop elements in the Page Inspector (additional information)

Web console command history is now persisted across sessions.

Fetch API has been activated (bug 1133861)

Firefox for Android

Firefox for Android shares the majority of changes with desktop versions of Firefox.The only Android-specific change lets you paste clipboard contents into editable web contents.

Security updates / fixes

MFSA 2015-71 NSS incorrectly permits skipping of ServerKeyExchange

MFSA 2015-70 NSS accepts export-length DHE keys with regular DHE cipher suites

MFSA 2015-69 Privilege escalation in PDF.js

MFSA 2015-68 OS X crash reports may contain entered key press information

MFSA 2015-67 Key pinning is ignored when overridable errors are encountered

MFSA 2015-66 Vulnerabilities found through code inspection

MFSA 2015-65 Use-after-free in workers while using XMLHttpRequest

MFSA 2015-64 ECDSA signature validation fails to handle some signatures correctly

MFSA 2015-63 Use-after-free in Content Policy due to microtask execution error

MFSA 2015-62 Out-of-bound read while computing an oscillator rendering range in Web Audio

MFSA 2015-61 Type confusion in Indexed Database Manager

MFSA 2015-60 Local files or privileged URLs in pages can be opened into new tabs

MFSA 2015-59 Miscellaneous memory safety hazards (rv:39.0 / rv:31.8 / rv:38.1)

Additional information / sources

Now Read: Firefox Release Schedule

Summary Article Name Firefox 39: Find out what is new Description Mozilla released Firefox 39, a new version of the web browser. This guide provides you with detailed information about new features and changes. Author Martin Brinkmann

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