Is it safe to use normal CFL Lightbulb on a houselight, that has a dimmer switch?

Most CFL's are not designed to dim. They are either "on" of "off". There are dimmable CFL's available, but they don't work as well as incandescents. There are subtle voltage variations in your service, and this may result in the light unexpectedly turning on and off. It's not a safety issue, it's a functional issue. Hope this helps.