I've never heard of a capacitor rated by "millifarad." A "1 millifarad" capacitor would be marked as 1000 microfarads.
Dimensions don't always tell the tale either. When I was in electronics class ('72-'73) one of the excercises we had to do was calculate dimensions for a workable ONE FARAD capacitor. The smallest unit anyone came up with was about the size of an eighteen-wheeler.
Nowadays, with new materials & such, the extreme bass-thumping idiot drivers have BANKS of ONE FARAD (rated ~15V) caps in the line (each about the size of a tall-boy can of beer) to help fill in the power gaps of the subs. I also have some ONE FARAD caps that aren't much larger than a coat button (rated ~5V).
Things may have changed some, but my recollection is that caps are marked in microfarads, picofarads, or (now) farads in non-fractional numbers. That way there's no room for confusion about what a "m" stands for.
But, I could be wrong.....
FWIW
Scott