Fixture on ceiling in my scene has material with light emission on it, but it's very weak. Light source that simulates flashlight near camera, is corona light. It's small (20mmx5mm) and extremely powerful - 20K units of intensity. I tried to change its shape to sphere, but fireflies grew up in orders of magnitude :]
My system units is in mm.
I decided to make very simple scene to experiment more with caustics and after many tries and errors, i found one way to completely get rid of these nasty bugs. I found that setting glossiness value to 1, in reflection and refraction, gives fireflies free image. Now i'm trying to fix all materials in my main scene. Will see if it works in more complex scene.