Texture filtering will help because firefly will then use a downsized resampled texture version that's more fitting for the small size of the hair compared to the size of the texture. But for Poser 5/6 texture filtering means 3 times as much memory usage for each texture. So if you're running out of memory when using Poser 5/6's firefly, try downsizing the hair textures with an image editing software.