Internet Explorer (IE) and Netscape handle mime type detection in different ways, and therefore will display the document differently. In particular, IE sometimes relies on the file extension to determine the mime type. This can happen when the server specifies a mime type of application/octet-stream or text/plain. (Unfortunately, this behavior makes it impossible to properly send plain text in some situations unless the file extension is txt.) There are more details available on IE's mime type detection behavior in an MSDN article.

In order to make all browsers work correctly, you should assure that Apache sends the correct mime type for the file. This is accomplished by editing the mime.types file or using an AddType directive in the Apache configuration files.