Upon a closer inspection, now that it is Monday. This is exactly what
is printed on them.

MF 20.0uF 250V AC K

The blown one has a almost waxy stuff on the outside, I don't know if
that is due to failure or careless assembly years ago. The good one,
looks clean and clear with no residue.

I'm thinking they decided to us MF to signify Metalized Film? Nothing
else I can think of makes sense to me(well there is one thing...). I
know the K is for 10% tolerance.

They yellow outer package is either a plastic or resin shell. On the
failed unit it is brittle and breaks off easily (I probed it with a
plastic feeler to see if it was bubbled out or just some gunk on it).