different speed on different devices !!!

pleas help i completed the game long time ago but this is the last problem before publishing the game. and it’s been a months of searching and asking and i didn’t fixed it.
i have simple objects moving from right to left and there is a very simple script attached to them :

using UnityEngine;
using System.Collections;

public class Mover : MonoBehaviour 
{
	private float movspeed = 10f ;

	void FixedUpdate () 
	{
		rigidbody2D.velocity = new Vector2 (-movspeed ,rigidbody2D.velocity.y);
    }

}

note : i used delta time with Update & FixedUpdate and the result is the same.

i suppose that it vary’s according to the speed of the device’s processor, however, your code is perfectly fine. that’s what i think about it.