Is Chlorofluorocarbon (freon gas) a threat to the ozone layer?

Absolutely.

UV rays (light photons) cause the bond breakage between the carbon-chlorine bond in a typical CFC like CCl3F. This reaction proceeds as:

CCl3F CCl2F + Cl-

The chloride ion is very unstable in the upper atmosphere, and causes ozone to break down into simple O2 molecules. These do not absorb UV radiation from the sun nearly as well as ozone, so high energy radiation floods the planet. You should read the Wikipedia article on this, as it is very descriptive.

Freon is a brand name for many molecules that contain at least fluorine.  Not all freons contain chlorine.

If you'll note, ozone is heavier than air, yet it is found in the ozone layer at levels 100 times what is found at Earth's surface.  If you'll look at the news, you'll note that volcanic ash is found at 20,000 feet and even higher.  This stuff is much denser than the heaviest gas (WF6 at room temp).

Diffusion does not care about how heavy trace amounts of gas are.  CFCs have been observed and even directly sampled to be at the elevation of the ozone layer.  Man makes them and the Space Shuttle did not dump them.

These gases will diffuse to the level of the ozone layer, where the UV will destroy them, releasing the chlorine, and for a time, decreasing the equilibrium concentration of ozone.  This will repeat for each chlorine or bromine containing gas until they are all gone.

Nature does not care what you don't understand.  It is up to you to do some research.