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Firefox Beta

September 5, 2018

Version 63.0beta, first offered to Beta channel users on September 5, 2018


  • 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

  • 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


  • Changes affecting developers

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

  • Added support for Web Components custom elements and shadow DOM

Developer Information


  • Quick Heal internet security software might crash 32-bit Firefox on Windows