The root cause of this bug and bug 1588821 appears to be that in Catalina our content processes need to access ~/Library/Preferences/.GlobalPreferences.plist, but are prevented from doing so due to sandboxing. In that plist, the tab key setting and the scrolling behavior setting (bug 1588821) are saved as AppleKeyboardUIMode and AppleScrollerPagingBehavior respectively. Something in Catalina must have changed to make the plist be accessed after the sandbox is enabled. That needs some more debugging and comparing with earlier releases to confirm. I am testing a fix that addresses both issues and should have something for review tomorrow.
Bug 1587962 Comment 9 Edit History
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The root cause of this bug and bug 1588821 appears to be that in Catalina, in Apple code, our content processes need to read ~/Library/Preferences/.GlobalPreferences.plist, but are prevented from doing so due to sandboxing. In that plist, the tab keyboard focus setting and the scrolling behavior setting (bug 1588821) are saved as AppleKeyboardUIMode and AppleScrollerPagingBehavior respectively. Something in Catalina must have changed to make the plist be accessed after the sandbox is enabled. That needs some more debugging and comparing with earlier releases to confirm. I am testing a fix that addresses both issues and hope to have something for review tomorrow.