JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
 <div id="centered-item">
  <div id="positioned-item">
  </div>
 </div>
</div>
<pre>

  This bug is visible in Firefox.

  The blue box should have a 'left' value of 100px, but due to the
  rounding to fix ticket #5280, it gets the incorrect value 100.5px

</pre>

CSS

#container {
 position: relative;
 background: red;
 width: 575px;
}
#centered-item {
 position: relative;
 background: green;
 width: 150px;
 height: 100px;
 margin: auto;
}
#positioned-item {
 position: relative;
 background: blue;
 width: 50px;
 height: 50px;
}

JavaScript

$('#positioned-item').position({
 of: $('#centered-item'),
 at: 'right bottom',
 my: 'right bottom',
 offset: '0 0',
 collision: 'none none'
});