It is a frequent UI design for a range slider to showcase the immediate change in the depicted value as the user moves the slider. This is not the case for the above-mentioned browser (chrome included).
Although, one could argue that Firefox showcases the correct behavior because the onchange event executes only when the control loses focus (be it mouse drag or keyboard). But in order to display the changing value along with the moving slider, one needs to apply the oninput event attribute.
Oninput: Much like the onchange event, this attribute works when it receives user input value. The main difference being its immediate execution when the value of element changes.
<element oninput = "script">
Program to illustrate Solution: