Border size as 0.667 when set the border width as 1px in FireFox

In FireFox browser alone , i get the border size as 0.6667 when i set the border width as 1px to the div or input element or any HTML element. Please find the below screenshot.

I have given the border in css inline style and also via separate class but i get the same result. i have not provided any box model to the element.

If i given the border size 2px then its working fine. i get problem on providing odd number.

if i give 1px => 0.6667
if i give 3px => 2.6667

Due to above problem, my calculation get breaks in css level. So can you please provide solution to resolve this issue?

Whether its browser issue? or else provide any work around solution on this?