Window condensation happens when warm moist air comes in contact with a cooler surface. If turning down the humidistat on your humidifier does not help, consider the other sources of humidity in the home.
Use the kitchen exhaust fan when cooking and the bath fan when showering. Space heaters and vent-less fireplaces create a lot of humidity. Make sure the attic is properly ventilated and check the crawl space for dampness. Home is too tight article.
The moisture along the edges of your windows is caused by excess humidity in the home. It can be intensified by air leakage along the edges of the window frame that cools the glass. This condensation can cause a mold to form over time.
Get a hygrometer, under $15, from your local hardware and check the humidity in your home. If your indoor humidity is over 35% I would expect to see a little condensation around the windows.
More humidity usually translates into greater comfort; Mrs. Hardware keeps our humidifier on jungle, but greater attention must be paid to possible moisture problems.
If you have been insulating, caulking and otherwise tightening up your home, you may need to add a make-up air unit to replace air in your home. Air leakage around the windows is an indicator of negative pressure in the home. Your furnace, hot water heater, clothes dryer, kitchen and bath fans all exhaust air to the outside of the home; but where is the replacement air coming from?
All too often the replacement air comes through gaps in windows and doors, chilling the edges and causing condensation.
To remedy this situation, add a make-up air unit to your furnace and utility room. One company, EQUALIZ-AIR uses two four-inch ducts to supply make-up air to the house; one connects to the furnace cold air return and the other to the utility room for the dryer.
Now your appliances will be using outside air to operate rather than expensive inside air you paid to heat or cool.
Use oxygen bleach to clean up the mold and mildew on the frames of your windows. Mix it per the instructions and apply two light coats about five-minutes apart. Then rinse with warm water and dry.
You should add a mildewcide to your next finish coat of paint or varnish to prevent further mold from forming.