Box-Sizing: How to Get Rid of the Scrollbar Padding in Firefox

Remove scrollbars Firefox desktop

The scrollbar behaviour is Fixed in Firefox 57

Firefox ignores padding when using overflow:scroll

in Firefox padding-bottom is ignored with overflow:auto or
overflow:scroll, see the documentation

https://bugzilla.mozilla.org/show_bug.cgi?id=748518

still if you want to work around your example to achieve the desired result then see the fiddle: https://jsfiddle.net/nileshmahaja/4vuaf4o3/1/

Modified CSS

.container {
    height: 200px;
    padding: 50px 50px 0;
    border: solid 1px red;
    overflow-y:auto;
    display:block;
}
ul{
    padding:0 0 50px;
    display:block
}
li {
    padding: 0;
    margin: 0;
}

firefox issue with the padding-right of the container box

Add an extra div that wraps your existing div and do float:left.

<body style="margin: 0; padding: 0; overflow-y: scroll;">

<div style="background-color: pink; width:100%;float:left;">
<div style="background: pink; padding: 32px; float:left;">
<img src="http://projects.quantize.com/P/reporter/blog/wp-content/themes/thesis/rotator/sample-1.jpg" style="width: 640px;" />
</div>
</div>

</body>

Edit: Removing display: block; as that's irrelevant when you have float.

Hide scroll bar, but while still being able to scroll

Just a test which is working fine.

#parent{
    width: 100%;
    height: 100%;
    overflow: hidden;
}

#child{
    width: 100%;
    height: 100%;
    overflow-y: scroll;
    padding-right: 17px; /* Increase/decrease this value for cross-browser compatibility */
    box-sizing: content-box; /* So the width will be 100% + 17px */
}

Working Fiddle

JavaScript:

Since the scrollbar width differs in different browsers, it is better to handle it with JavaScript. If you do Element.offsetWidth - Element.clientWidth, the exact scrollbar width will show up.

JavaScript Working Fiddle

Or

Using Position: absolute,

#parent{
    width: 100%;
    height: 100%;
    overflow: hidden;
    position: relative;
}

#child{
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: -17px; /* Increase/Decrease this value for cross-browser compatibility */
    overflow-y: scroll;
}

Working Fiddle

JavaScript Working Fiddle

Information:

Based on this answer, I created a simple scroll plugin.