How long will a browser remember a "a:visited" link? Assuming the method isn't uniform across browsers - an answer for any individual browser (or as many as you know) would be helpful.
Also, under which type of memory is it stored? "Web History"? Cache?
Visited links are part of your web history, and how long they're stored depends on each user's individual browser settings. I believe Firefox remembers unlimited history by default, but anyone can set a time limit on it, or have it be cleared every time they close their browser, etc.
Usually, it's :visited if the url is in the browser's history, this is pretty consistent across browsers. How long?...however long history is stored, which varies greatly depending on preferences. Also, if the user's in any sort of privacy mode, history is typically disabled, meaning no links are "visited".
Not sure about all browsers, but Firefox seems to show visited links in different color until I restart the browser; it shows these visited links in history tab, but they are the same color as visited on the page.