1. Some sites refer to zero-size images on other hosts to keep track of cookies. When IceWeasel detects this mechanism it blocks cookies from the site hosting the zero-length image file. (It is possible to re-enable such a site by removing it from the blocked hosts list.) 2. Other sites rewrite the host name in links redirecting the user to another site, mainly to "spy" on clicks. When this behavior is detected, IceWeasel shows a message alerting the user. Reproducible: Always
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