You can use Stylish/Stylus extension or just plain vanilla usercontent.css in your Firefox profile:
@-moz-document domain("www.reddit.com") {
div[style*="max-width"] div[class] > div:not([class]):nth-child(20n) {
border-bottom: 4px solid red;
}
}
Of course it can be used as userscript too:
// ==UserScript==
// @name reddit mark
// @grant GM_addStyle
// @match https://www.reddit.com/*
// ==/UserScript==
GM_addStyle(`
div[style*="max-width"] div[class] > div:not([class]):nth-child(20n) {
border-bottom: 4px solid red;
}
`);
Adding a virtual pagebreak in Reddit
I don't like the endless scrolling on the new version of Reddit, I'd love a script would insert a mark/line every 20 posts so I could see how many posts I've scrolled through.