Don't manipulate the DOM while traversing it. http://dev.opera.com/articles/view/efficient-javascript/?page=3#traversemodify

manipulating-after-traversing.js

var
allPara = document.getElementsByTagName('p'),
collectTemp = [];
for ( var i = 0; i < allPara.length; i++ )
{
  collectTemp[collectTemp.length] = allPara[i];
}
for ( i = 0; i < collectTemp.length; i++ )
{
  collectTemp.appendChild( document.createTextNode(i) );
}
collectTemp = null;

manipulating-while-traversing.js

var
allPara = document.getElementsByTagName('p'),
i;
for ( i = 0; i < allPara.length; i++ )
{
  allPara.appendChild( document.createTextNode(i) );
}