Font-size buttons

I came upon this trick: a usemap with two buttons for
changing the page's font size:

============
<map name="fontmap" id="fontmap">

<area shape="rect" coords="111,1,126,15"
href="http://niemanwatchdog.org/index.cfm?fontsize=up";>

<area shape="rect" coords="127,0,143,14"
href="http://niemanwatchdog.org/index.cfm?fontsize=down";>

</map>

============

The page itself is: http://niemanwatchdog.org/index.cfm

Two questions: (1) how does it work? New pages?
What's the question mark ( "cfm?font..." ) do?

and (2) is this idea useful?

The user *may* have the ability to change font size or
do a zoom in the browser.
This page button trick may be more convenient.

Mason C

.