all of these guys are right, i will try to explain a way so you have perfect results.
in very hot weather, pre sprey the glass first, this will lower the temp and enable you to clean and rinse without the water drying too quickly.
if you think its powdery milky stuff from the top frame this is how i do a first clean on these, setting you up for the futer cleans)
1. scrub that top frame, really hard and fast, get that oxidisation gone, from left to right
2. scrub the side frames and the window cill, give the windowsil a nice scrub becasue you cant see the green on upper windows.
3. scrub the top frame again and rinse and clean just the top four inches of the glass
4.scub the rest of the glass dont bother rinsing, let the water soak in an do the work for you
5. leave this window and do this process with a few more windows.
6. go back to the first window and clean only the glass as normal, however imagine the top of the window is the top four inches that you have already cleaned and rinsed. (miss the top four inches)
7 . turn your flow off and wipe the sill
8. when you come back next time, clean window as normal