It actually depends on the car: Most catalogues will tell you Driver's side to be 22" and Passenger side to be 20". Some actually say 19" for the passenger side.
You should use a 22"/19" combo on the 95-98 'tours
a 22"/20" combo on the 98.5 SVT's and 99-00 'tours
here's why; from 95-98, the used what they call a 9X4 style hook with bosch SWF blades. The passenger side wiper arm with the 9X4 hook is actually about a 1/2 inch longer than that of the newer wiper arm which is called a 9X3 hook (the hook itself is smaller. All of the MKII mondeos stayed with the 9X4 hook while when ford USA started using the 9X3 hook.
if you use 20" blades of some brands (depending where your passenger side wiper arm rests) it will hit the corner of the windshield causing the wiper to wear quicker..
I'm sure that's more than what you wanted to know... but it's my .02
Oh yeah, about the refills, if you have the origional bosch swf blades (95-98), the old style Bosch Micro-Edge, the old style Bosch Micro-Edge Excel, or the origional Valeo ("Smart Blade") Kmart's Penske Narrow refills are a direct replacement for the narrow "trapezoid" style retainers. They're cheaper than the bosch there is no retaining clip to get in the way....