Works really well, auto-hides scrollbar in the latest firefox. However, if you browse to an old reddit subreddit that uses a custom old subreddit style, like /r/ffxiv, the custom style will scroll with the page, detached from the subreddit.

It is also incompatible with current YouTube, and disallows scrolling on YouTube.

the scroll bar changes colors whenever I refresh the page

The implementation seems a bit bloated with by loading the whole jQuery library just for this, and including a backup file in the extension (which is useless to users).

But it works well!