I think it's not the font size, so much as the "line-height" property in CSS

Unfortunately, I don't know of an easy way to customize line-height in browser preferences.

At some point, once the dust has settled, the DU admins may have time to fine-tune the site's CSS (Cascading Style Sheet) to address issues like this.

Wikipedia has a nice explanation of line height, or what is termed "leading" in the printing biz:
http://en.wikipedia.org/wiki/Leading

Includes a good visual example of a block of text with no line-height property/leading specified, and the same block with the property specified.

Gives the text much more breathing room, so to speak, making it much easier on the eyes, IMO.


More about CSS (Cascading Style Sheets):

http://www.w3.org/Style/CSS/Overview.en.html

http://www.w3schools.com/cssref/default.asp