An online algorithm to maintain the Pareto frontier elements
You can find an answer to this in "Dynamic Planar Range Maxima Queries", by Brodal and Tsakalidis. They support insert and remove in $O(\log n)$ time. That paper points to several previous papers that addressed the question as well.

In particular, I expect the simplest solution can be found in sections 8 and 9 of "Maintenance of Configurations in the Plane", Technical Report RUU-CS-79-9, by Overmars and van Leeuwen, (mirror). Their solution takes $O(\log^2 n)$ for each insert or remove.