border-collapse:collapse set border-top-width set to 0px or 0.5px

border-collapse:collapse set border-top-width set to 0px or 0.5px

Hi, I think this is all ready reported but i cant found a sollution or reason why this happend. 

My problem is as followed. 
I got a table with this stylesheet: 

table { 
      border : none; 
      font-size : 12px; 
      line-height : 20px; 
      width : 100%; 
      border-collapse : collapse; 
      border-spacing: 0; 
} 

th, td {
      border-left : solid 1px #E2E2E2; 
      border-top : 1px solid #E2E2E2; 
      color : #231F20; 
      padding : 10px; 
      text-align : left; 
      vertical-align : middle; 
      white-space : nowrap; 
} 

know when i call in jquery the following: 

$('table').find('th').first().css('borderTopWidth'); 

the response in the following browsers is as followed: 
      webkit : 1px; 
      IE : 0.5px; 
      Gecko : 0px; This one is at this moment the biggest problem know 

i can find that this happend to a lot of peoples but i can't find the solution or the reason why this happend. 
Has anyone have answer for me? 

With kind regards, 

Michel