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How do web browsers remember which links have been clicked (and thus, color them purple/differently)?

As of this week, all links in my Google searches have suddenly turned purple, as if they've all been clicked before (even ones I've never clicked). Clicking them doesn't change the color.

My musings --

Is it merely a direct comparison of displayed links to the user's browsing history (handled by the browser)? Is there some sort of clicked-link cache? Is the information local, or is there server involvement (like with headers/cookies)?

Note:

I'd prefer to keep my browsing history and not have to wipe/clear it in the hope that it'll somehow fix the issue. Hence why I'm trying to get at the heart of the issue by backtracking how the links are colored purple/blue in the first place.

In a couple of cursory Google searches, it appears that others are having this problem, and even as of 2013-07-05.

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This is happening in Firefox and Chrome? – AthomSfere Jul 5 '13 at 18:07
    
This sounds like the expected behavior: links that have been visited are colored purple. Am I misunderstanding something? – Ryan Jul 5 '13 at 20:15
    
I believe it is down to the user's browsing history. The information is definitely stored locally: it does not make sense to involve servers. Before you begin to debug the situation, you could either export your history or make a copy of your profile. I've seen the same issue reported elsewhere, and I have once experienced this issue myself on a clear (unused) profile on a Nightly build. I tried a new profile and I could not reproduce the issue. I don't really know what to say about this behaviour. – Wk_of_Angmar Jul 5 '13 at 22:06

I tested this with Bing and Google search engines in Chrome and Internet Explorer. I initially thought it was just Google that did it, because I hardly ever use any other engine. I found that when I searched Stack Overflow in Bing, it was already purple in both Internet Explorer and Chrome after I had clicked the link from the Google engine (hopefully that's not too confusing).

With that being said, it is indeed each browser that manages the color, but I am very intrigued as to how it works as well. To test this, I then proceeded to clear each individual history item in Chrome's clear history setting and checked the color. To my surprise, when I checked the box "Empty the Cache" the link still remained purple after I refreshed the page. It was actually the box "Clear Browsing History" that returned the links to blue. I tried this in Internet Explorer as well, and the links only returned to blue when only the "History" check-box was checked and the browsing history was cleared, not the "Temporary Internet Files" or "Cookies" check-boxes.

So to answer your question, I would probably say that it is a direct comparison of the user's browsing history data. There could be more to it, but hopefully that helped.

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It just happened to me today using Windows 7 and Firefox 23.0.1. When I view Google search results, every result is purple (which supposedly means I visited every link already, which is definitely not the case).

The solution was to delete Google's cookies. You don't want to clear out all your cookies for all sites, otherwise you'll lose a lot of preferences and logins. In Firefox, go to menu Tools -> Options -> Privacy -> remove individual cookies (a link on that page). Find google.com and delete that. You'll have to re-login into your Google account.

After I did that, the links went back to normal (blue for unvisited links, purple for visited).

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