How can I seal old Jalousie windows?

I believe that if you purchased the 3/16" style of the vinyl strip and tried using it on 1/4" thick glass that you would be extremely disappointed with the result. The strip will likely not stay in position trying to pull it over the edge of the thicker glass. And even if it did a half-baked job of staying in place the flap that is to seal against the opposite slat will be cocked at a strange angle and may not even allow the slats to close properly.

I would search out a similar product made specifically for 1/4" glass slats.

Shrink film - works irrespective of window type. Apply doublestick tape around window frame, apply shrink film, heat with hairdryer or heat gun to shrink, remove in spring. Quite clear, quite effective, not very easy to remove/replace if you decide to open the windows in January, though it can be removed/replaced with care if you don't trim all the excess film when installing. "Shrink film window kit" will find a vast array in a search, or try your hardware store.

I have an idea. Use a rollup window shade mechanism. Put clear 2 mil to 4 mil plastic sheeting on it. Install thin steel strips around the window casement. Buy 1/2" magnetic strips that surround the entire 1 or 2 screen frame. This way, if you want to open the windows for clear air or natural ventilation, just pull off the magnetic strips, roll up the plastic.
Í have been thinking of this for a long time. I am putting on 2 mil transparent carpet protection plastic 36". It will curve over .4" and allow velcro on the frame to match the velcro patches on the plastic. Lets see how it works. Mike in Miami.