Here's how to do it:
For Firefox visit the GreaseMonkey manual and look up how to install GreaseMonkey and user scripts. These are pretty easy to do and when you are done, install this script:
if (window.location.hostname.match("livejasmin.com") || window.location.hostname.match("888.com")) window.close();
This script checks every time a new page is opened if it's one of the unwanted pages (you can add more, of course), and if so, it closes it instantly.
Google Chrome has a built-in support for scripts, so you can use that. Opera ditto. Explorer too.