Let’s say you’re on a news website for instance bbc.co.uk, that you read a lot, but each time you look on the website you can’t tell if you already visited that portion of the website or not.
Let’s say you still have a chance, there’s a Firefox and Chrome add-on called Stylish.
First you need to install it, then create a per/site style. For example bbc.co.uk website adds a story class to each link that refers to a story,
so you just need to add:
to your custom style, then hit preview.
If you’re happy with the changes give it a name and save it.
The next time you’re going to your favorite website that customized CSS will be added by your browser.