I guess the problem is related to HTTPS-Everywhere rewriting http urls to the corresponding https version. Since not every url gets rewritten (even for the same domain) I did not notice the correlation.
This issue has to be dealt with HTTPS-Everywhere. This bug report can be closed here. ** Changed in: firefox (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/828391 Title: Some urls are not shown as already visited. Especially imgur urls with a rather short hash in the url. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/828391/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs