currentSize = 12;
function GetFontObject() {
       return document.getElementById("flexibleFont");
}
function Bigger() {
if(currentSize < 18)
         currentSize++;
GetFontObject().style.fontSize = currentSize + "px";
}

function Smaller() {
if(currentSize > 9)
         currentSize--;
GetFontObject().style.fontSize = currentSize + "px";
}

function Original() {
GetFontObject().style.fontSize = 12 + "px";
}