I just posted a question and I noticed that unvisited links use a color that is difficult to distinguish ... but visited links are even harder to recognize. See the snapshot below from my Firefox 41.0.2 (all default settings).
Does it look different on other browsers?
Let me know if this is not the right place to ask questions about the appearence of the site (I'll delete the question).
EDIT: after reading the comments, it's clear that there is an issue with the css style of visited/unvisited links ... is there a way to signal it to the web designers of mathoverflow?