Firefox Beta and Developer Edition
Release Notes

Added content blocking, a collection of Firefox settings that offer users greater control over technology that can track them around the web. In 63, users can opt to block third-party tracking cookies or block all trackers and create exceptions for trusted sites that don’t work correctly with content blocking enabled.

WebExtensions now run in their own process on Linux

Firefox now warns about having multiple windows and tabs open when quitting from the main menu. The Save and Quit feature has been removed. You can restore your session by ticking the box for Restore previous session in the General → Startup options or by using Restore Previous Session in the main menu.

On macOS, WebGL power preferences allow non-performance-critical applications and applets to request the low-power GPU instead of the high-power GPU in multi-GPU systems

Improved Windows 10 integration: your Firefox theme now matches your OS Dark / Light mode

Faster tab switching in the majority of cases for our macOS users

Improved the reactivity of Firefox on macOS

Resolved an issue that prevented the address bar from autofilling bookmarked URLs in certain cases

In the Library, the Open in Sidebar feature for individual bookmarks was removed

The option to Never check for updates was removed from about:preferences. You can use the DisableAppUpdate enterprise policy as a substitute.

The Ctrl+Tab shortcut now displays thumbnail previews of your tabs and cycles through tabs in recently used order. This new default behavior is activated only in new profiles and can be changed in preferences.

The build infrastructure of Firefox on Windows moved to the Clang tool chain, bringing important performance gains

Refreshed visual style of Developer Tools menus to improve navigation and consistency

The Dev Tools accessibility inspector is now enabled by default. This tool surfaces information exposed to assistive technologies on the current page, allowing you to check what’s missing or otherwise needs attention.

Added support for Web Components custom elements and shadow DOM

Quick Heal internet security software might crash 32-bit Firefox on Windows. A workaround is documented from this support article until a fixed version of Quick Heal is available.