The problem you have is caused by the fact that you're designing your web pages with a Microsoft HTML editor which takes advantage of features that the Microsoft browser supports, but others may not. Although Internet Explorer users vastly outnumber those with Netscape or others, I always try to design the web page for users of either. At the very minimum, I test with IE 5.5 and Netscape 4.75 to make sure they both render properly.
There are a tonne of other web page editors out there. I prefer Macromedia's Dreamweaver (http://www.macromedia.com), but it's a commercial product, so you'll have to pay. (Unless you happen to stumble across a working serial number.
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