Hi,
Is there somewhere that one can enter the URL of popup windows, in order to block them?
Thanks,
John

no.
but You can bar most popup windows by activating blocking in Preferences/Privacy.
& You can further reduce the number of popup windows by deactivating Java Script.

AFAIK there is no way to prevent the popups totally.

p. s. Java Script and Popups are needed by some Webmail providers /
many here activate Java Script only on pages they trust / deactivating JS is possibly also making the browser faster - I only activateJSt where i needed it
e. g. @Yahoo mail.

As guenter points out you can eliminate many popups by checking the box under Preferences-Privacy. You can also go to Advanced-Preferences-Content Filters to put a checkmark in CSS and Flashblock. This will also eliminate some popups. With Flashblock you will have to restore Javascript by putting a checkmark there.

There are many third party blockers that you can use. While K-M does support some versions of Ad Block, it is a bear to configure. A free utility is XP Anti-spy which has a number of things that controls XP's behaviour and popups is one of the things you can check off. I use Ad Muncher. For the most part is suppresses Ads, but it also has a popup component.

Thanks Guenter/Terry,
I appreciate the help.
John