Guess it depends on yer browser/printer/driver/resolution/OS
But apart from that it should be perfectly straightforward :) I know in Acrobat reader it has/had an option for showing 'greek text' below a certain size. Which isn't greek, just a way of saying 'there is text here but I can't accurately draw it'. So I guess some part of your system perhaps isn't giving the rest of it the credit it deserves for its ability to render text, and is just thinking 'Nah! Impossible! I won't even try!'
Someone who actually knows about this stuff can possibly offer a slightly more plausible explanation...
Moz 1.5 and [smaller type] shows correctly in Preview
Save as post - NOT.
[CTRL + or -] of course, alters overall typesize.. in Moz and maybe others.
My bad, I said 'print' meaning 'print to file'. This acts as if there is a "min type size" filter twixt Preview and Save; it's also rel. new phenom, as that has worked in past.