Table Border Issue in both IE and Firefox

Just discover that when coding the following into style sheet:

table {
  border-collapse: collapse;
}
th, td {
  position: relative;
  border: 1px solid #eee;
}

In Firefox 3, top and right borders of each table cell will disappear.

In IE 7, borders could not collapse.

Don’t know why this happened, need to do a little bit more research.