Not much...
I know that Boeing developed Nitrogen Gen Systems (NGS) to inert the center wing tanks (and, IIRC, the wing tanks for the 787 since the carbon composite construction tends to insulate the fuel and keep it at a higher (combustible) temp longer than metal wing tanks). Further, somewhere around 2010 all new production aircraft had NGS systems installed, and retrofit kits were made available for in-service aircraft.
My limited understanding of the original FAA fines was related to Boeing rather seriously underestimating the difficulty of developing commercially viable NGS systems and missing the originally agreed to dates for production and retrofit availablity (apparently the NGS hardware proved rather unreliable in the service demonstrator tests and it took a lot of time and money to get them up to the reliability necessary for commercial airlines operating 8-12 hours/day for over 20 years).