onmouseover problem with HTML table

I am trying to use the onmouseover event with an html table cell.  It works fine in IE, but not in FireFox

For testing I am using the following code

<SCRIPT type="text/JavaScript">
  <!-- hide

function FillCalGrid(Nme)
  {
alert(Nme); 
}
  // stop hiding -->
</script>

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And the HTML is

<A href="##" onmouseover="FillCalGrid('M1')"><TD vAlign=top width="13.13%" bgColor=#Trim(SetColor(GetShifts.Shift1))# ID=M1 onClick="addCalColor('M1')"><br><br>&nbsp;</TD></a>  

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(The HTML above is just for one cell, but the same is repeated several times with different cell IDs
I am coding in ColdFusion hence the #s.)

In Firefox the addCalColor and SetColor routines fire correctly, but the onmouseover event never fires.

If I add "This is a test" just before <TD... , the text appears, and when I hover over the text the onmouseover event fires as it should, but it will not fire for just an empty table cell.

What am I doing wrong?