A solution for anyone who wants to increase the size of Firefox fonts in Kubuntu Hardy.

[Steven Vollom]

This solution works, however, when you choose minimum font size, you may 
want to use about 16 point.  Anything less still prints too small.  On 
the menu, click on edit -> Preferences -> content -> Fonts & colors -> 
Advanced -> change Min Font Size to one that is suitable.

It worked for me; it should work for you.

Caio,
Steven