In article <3274EC77.3C0A at Bris.ac.uk>, Andrew Doherty <A.Doherty at Bris.ac.uk> says:
When we methanol treat GFP transfected cells we also loose the
signal. However, on fixation with 3.7%formaldehyde and permebilization
with saponin a signal is still visable. Also I believe that GFP is very
labile, therefore any exposure to solvents results in a non-GFP. If your
cella are on a coverslip that needs to be sealed use low mp agarose instead
of nail varnish.