Changes

Note that a A 'level' value reflects unique sandbox security settings for each platform and process. Most processes only have two "active" levels, the current setting and a lower (previous released) setting. Level settings other than these two values carry no guarantee of altering security behavior, level settings are primarily a release rollout debugging feature. DEPRECATION WARNING - The current level system will be replaced by a configuration system that allows for more fine grain control over sandbox settings. Current target for this change is Firefox 57.