Testcase:

<div style="width: 0.33px"></div>
<script>
  console.log(document.querySelector("div").style.width);
</script>

In servo this logs "0.31666666px". It should really preserve the original "0.33px" value.

In Gecko, specified values are stored as floating point plus unit, and not converted to 1/60 px integers until computed value time.

And even then, note that servo above is converting by truncation, whereas Gecko uses rounding. Specifically, Gecko does NSToCoordRoundWithClamp which checks for overflow issues, then rounds to nearest via NSToCoordRound.