Discrepancy on left padding between Firefox and other browsers

[SYwaves]

Describe the issue:
On Firefox, there's an extra rule that add .5rem left-padding to the sidebar not present in other browsers.

@supports (-moz-appearance:none) and (background-attachment:local) and (not (-moz-osx-font-smoothing:auto)) {
  #side-bar {
    padding: 0 0 0 .5rem;
  }
}

Screenshot showcasing the issue:
Firefox:

Edge:

Notice the gap between the scrollbar and side-block.

Link to the page(s) having this issue:
https://scp-wiki.wikidot.com/theme:black-highlighter-theme

The extra rule could either be removed, or modified to effect same padding across all browsers.