How do I do it?

Thanks!

there's a tutorial on setting this up as a macro here:

http://kmeleon.sourceforge.net/docs/toggle.php

oh, and if you just want to change it once, you can just add a line like this to your prefs.js -

user_pref("font.size.variable.x-western", 22);

the default size is 16, so make the number larger or smaller than that according to how big you want the text to be.