<html xmlns="http://www.w3.org/1999/xhtml"> <head> <style> .container { height: 1em; } .overflow { height: 8em; } body { font-family: monospace; height: 8em; line-height: 1em; -moz-column-count: 2; -moz-column-gap: 0; } </style> <script> function boom() { document.documentElement.offsetHeight; document.getElementById('x').style.display = 'none'; document.documentElement.offsetHeight; document.getElementById('y').style.display = 'none'; } </script> </head> <body style="width: 17ch;" onload="boom();"><div id="x" class="container"></div>This paragraph must be in the first column.<div class="container" id="y"><div class="overflow"></div></div></body> </html>