642673 - FF4 previously visited link/icon does not change color as it did in prev versions

Status: RESOLVED WONTFIX

(Core :: CSS Parsing and Computation, defect)

Description

[enb]

User-Agent:       Mozilla/5.0 (X11; Linux x86_64; rv:2.0b13pre) Gecko/20110317 Firefox/4.0b13pre
Build Identifier: ubuntu maverick x64

I have only found one website where this happens so far: http://eztv.it/
On FF3.6, the download icons change color after they have been clicked. This no longer happens on FF4.

Reproducible: Always

Steps to Reproduce:
1. go to http://eztv.it/
2. click on the download icon for any random show
3. 
Actual Results:  
icon does not change color

Expected Results:  
icon should change color after being clicked as it does in 3.6

n/a

Comment 1

[Boris Zbarsky [:bzbarsky]]

This is a purposeful change.  The site is using different background-image styles for :link and :visited, and we no longer allow that to protect user privacy.  See http://dbaron.org/mozilla/visited-privacy for the details.

Comment 2

[enb]

(In reply to comment #1)
> This is a purposeful change.  The site is using different background-image
> styles for :link and :visited, and we no longer allow that to protect user
> privacy.  See http://dbaron.org/mozilla/visited-privacy for the details.

So, the way that the server can know if a user has visited a link before is by logging whether a browser downloads the image for the previously visited icon vs the non visited icon?
Are there any workarounds for this, so that privacy can be maintained while still showing a different icon, or a way to turn this off?

Comment 3

[Boris Zbarsky [:bzbarsky]]

> is by logging whether a browser downloads the image for the previously visited
> icon vs the non visited icon?

Correct.

> so that privacy can be maintained while still showing a different icon

Unfortunately, no.

> or a way to turn this off?

Also no.

Comment 4

[Christian]

The anchor tag change color depending on css attribute but it doen't change other attributes (i.e. backround-position)
<syle>
a.read-more {
	color: #bb0000;
	font-size: 12px;
	padding-right: 14px;
	background: transparent url(images/some-image.png) right top no-repeat;
	text-decoration: none;
}

a.read-more:hover {
	color: #00bb00 !important; /* important required to highlight the anchor again */
	background-position: right -18px !important;
}
a.read-more:visited {
	color: #0000bb;
	background-position: right -36px;
}
</style>

It works in firefox, but not in firefox 4.0

Comment 5

[Boris Zbarsky [:bzbarsky]]

Christian, you did read the link from comment 1, right?

Comment 6

[Christian]

Yes, Boris, it is clear, but text color still change!

Comment 7

[Daniel Holbert [:dholbert]]

> but text color still change!
Yes -- but only visually.  Web pages themselves can't detect the color-change, because we make getComputedStyle & friends lie.

Color is specifically allowed to be different because it doesn't affect page-layout or page-rendering-time, so web pages can't use sneaky non-getComputedStyle methods to try to detect whether it's changing.

Comment 8

[enb]

Won't the website hosting the image to be color changed already know if the link was previously visited by using cookies or unique links to identify the user? Google already uses stealth links that do not match what the status bar says when you hover over them to track what you've visited. How is this any different?

Comment 9

[Boris Zbarsky [:bzbarsky]]

The difference is that before the changes made to :visited you could check whether random links that do NOT appear on your site normally were ever visited by the user.  Try http://browserspy.dk/css-exploit.php in Firefox 3.6 for example.

Comment 10

[Christian]

I understand the reasons for a :visited {backgroung-image} method, but not for a :visited{backgroud-position} method. It seems to me the position method doesn't involve any further request to the server

Comment 11

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Drawing different parts of an image could have different performance characteristics, especially if some of the positions involve having the image where there's actually nothing to display.