The tracks around the frame might need replacing or lubing. Try some talcum (baby powder) powder 1st - not a long term solution but it will tell you if it is the problem. Just liberally powder the edges of the glass and see what happens. And before some one else says it at worse you'll have powder windows instead of power windows.

You could try graphite powder but that's dirty and doesn't smell as nice as talc. Seriously talc is a good dry lubricant.