Why Firebug on Firefox shows "border-width: 0 1px 1px" but Computed Style shows 1.1px?

Question

Firebug shows that the style is:

#summary-border {
  background:url("/images/gamma/backgrounds/product.gif") repeat-y scroll right bottom transparent;
  border-color:#D0D0D0;
  border-style:solid;
  border-width:0 1px 1px;
  display:inline-block;      /* this one is shown to be overridden */
  overflow:hidden;
}

But computed style shows border-right-width as 1.1px !?!? (the border-left-width also)

(Update: my coworker just told me it only happens on Firefox on Mac, but not on Linux or PC. And the Firefox I am using is the latest one: Firefox 3.6.11)

It isn't a problem except the width of that div is then made to 957.8px instead of 958px, and the other floated divs needed 958px and so a big pane can't float (because of 0.2px shorter than needed and that div wrapped under the other floated divs)

---

(more details:)

The original code in the css file is:

#summary-border {
  overflow: hidden;
  display: inline-block;
  border-width: 0 1px 1px 1px;
  border-style: solid;
  border-color: #d0d0d0;
  background: transparent url("/images/gamma/backgrounds/product.gif") repeat-y bottom right; }

Answer 1

Px in CSS do not describe absolute screen pixels. They are affected by the density of the display. You can read about the details in the CSS-spec.