It seems to me that you want the tabs an exact height but you haven't specified a height or line-height and so browsers will vary.
Try setting a height.
Code:
#nav_menu{height:41px}
Or at the least control the line-height so that it is consistent between browsers.
BTW this code is redundant.
Code:
*,h1,h2,h3,h4,h5,a,li,ul,p,ol,img,table,div,form,fieldset,button,input,body{ margin:0;padding:0;border:none;text-decoration:none;color:white;list-style-type:none;}
The universal selector on its own will do all that
*{etc...}.)
However you should be careful with removing padding and borders from form elements because many browsers will not let you re-instate the defaults and indeed the look of form controls will change of you remove borders. That's the reason that the universal selector was rejected in favour of more precise reset systems.
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