how to change fonts in tool bar of any app

[Fun Kid]

Hello all,

How can I change the font in the tool bar menu in any
application?  To be precise, I would like to change the font of
the text on the menu which says File, Edit, View, Options, Tools
and Help (in the case of my Thunderbird).

Edit -> Preferences -> Display -> Fonts (in the case of
Thunderbird) changes the font in which the contents of my emails
are displayed but I cant figure out a way to change the tool bar
menu text font.

I am using Ubuntu 6.06 with KDE as my desktop.  I have tried
going to System Settings -> Appearance -> Fonts and change all
the fonts but I did not notice any changes to the tool bar text.
Please help.

Thanks in advance.
Fun Kid