This bug is corrected. Maybe you have a older copy of jqGrid. Download the last revision from:
http://www.trirand.com/jqgrid/js/jquery.jqGrid.js

If you run the examples from this site with FF, do you have such problems?

I left out:

cellpadding=”0″ cellspacing=”0″

on the table. Adding that solves the problem.

There is still some misalignment between header table and row table cells. This is more visible is the total width exceeds the page width say of 1024px.

I had to fix this bug by adding the style element to the header table.
$(grid.hTable).css({width: grid.width+”px”, marginRight:”20px”});
after creating the
grid.hTable = document.createElement(“table”);
at in grid.base.js

If the change is valid you can make it part of next release.
I am working on 3.1

Thanks
Sachin Mittal