One way to identify where the fireflies are coming from is to render the scene using AOVs.
Open the Render Settings Window and select the AOVs tab. In Inactive AOVs, double-click on specular_direct, specular_indirect and specular. These new AOVs should appear under Active AOVs.
Render the scene and open the AOVs or render them in the IPRwindow (select the AOV from the AOV drop-down in the IPR window.
