I called DOW this morning and asked them if the acetone they recommend
for cleaning uncured Great Stuff foam will damage a vinyl window.

DOW's answer: "It's highly unlikely that the acetone will damage the
vinyl, but you should check with your window manufacturer since they
are responsible for the warranty on your wndows."

I called Simonton and asked them the same question. The first level
CSR went off to check with someone else and came back with "The
acetone will not damage the vinyl."

I'm going to email them with the same question to see if they will put
that in writing.

They are wrong. Acetone may initially not show harm but over time will
soften and warp the vinyl.