I haven't had enough firefly issues to need to use the hotpixel slider yet.
What lighting are you using? Sunlight, an environment map or emitters?
Sometimes hotpixels are just a glossy with too much specular - so reduce the specular or bump in that case.
I've also found that there fireflys can take longer to be rendered out of HDR enviro maps as opposed to LDR maps. And they can take longer to render out when using color emitters rather than blackbody.