It is well-known that Serif fonts are far easier to read than Sans-serif, particularly on-screen, or in dense text.

Is it possible to set the K-M default variable-width font to something other than Arial?

Edit C:\Program Files\K-Meleon\defaults\pref\winpref.js (make sure K-Meleon is not running). If you read pages mainly in English, I think the x-western font group is most important, but you should probably also edit some other groups.