before I can put the mouse pointer on the "x" the window pops to right, hiding "x" again

Sounds like an irritating bit of Javascript, Bill, kicked off by screen events (mouse movement).

Either
1. Disable Javascript (you may well find you don't lose much, depending on the sites you visit). Don't have Netscape handy currently, but I think it's straightforward.

2. Close window using keypad rather than mouse. <ALT>+<F4> is probably the easiest way of doing this in Windows.

3. Get ad-blocking software. This will also do away with banner ads, and/or prevent them dancing around too much. I find it a considerable shock when I turn off AdsOff these days. Down side is it costs, though not necessarily much when you consider the benefits.

4. Get a browser that can block pop-ups, as suggested by others. Mozilla is free, but I'm an Opera fiend and have not for one instant regretted having paid for the ad-free version. It's also more like Netscape than IE (based on the same code I think), so the transition may be easier for you. And it's fantastically more efficient and economical than any other browser, though here I'm starting to really show my bias.

Non-related and non-integrated advertising on the Web is a pet hate of mine, as is character profiling by the use of cookies. But don't get me started.