On bibliotek.dk we use JavaScript for popup windows (e.g. help and request) because we find it user friendly.
You have to allow popups and JavaScript in your browser.

InternetExplorer
Use: Internet options - Security - Custom level - enable Active scripting.
Allow popups: Internet options - Privacy - Turn on Popup Blocker.

Firefox
Options - Content - Uncheck Block popups windows.
Close a popup window by clicking Close or Alt-F4.