One of

• not_controllable: cannot be controlled by any extension
• controlled_by_other_extensions: controlled by extensions with higher precedence
• controllable_by_this_extension: can be controlled by this extension
• controlled_by_this_extension: controlled by this extension

The scope of the Setting. One of

• regular: setting for the regular profile (which is inherited by the incognito profile if not overridden elsewhere),
• regular_only: setting for the regular profile only (not inherited by the incognito profile),
• incognito_persistent: setting for the incognito profile that survives browser restarts (overrides regular preferences),
• incognito_session_only: setting for the incognito profile that can only be set during an incognito session and is deleted when the incognito session ends (overrides regular and incognito_persistent preferences).

Only regular is supported by Firefox at this time.