Version 63.0, first offered to Release channel users on October 23, 2018
Performance and visual improvements for Windows users
Moved the build infrastructure of Firefox on Windows to the Clang toolchain, bringing important performance gains
Firefox theme now matches the Windows 10 OS Dark and Light modes
Performance improvements for macOS users
Faster tab switching
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
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.
Firefox now recognizes the operating system accessibility setting for reducing animation
Added search shortcuts for Top Sites: Amazon and Google appear as Top Sites tiles on the Firefox Home (New Tab) page. When selected these tiles will change focus to the address bar to initiate a search. Currently in US only.
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.
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.