Netscape won use QuickTime to play QuickTime movies. Is this because of Plugger / XSwallow / Xine?
Check the About Plugins page to make sure the QuickTime Movie (.mov, .qt) entry is enabled. (Note that there are several QuickTime entries, the video/quicktime MIME type is the one this plugin handles). The right-hand column for this entry should be YES. If not, another plugin may have already been setup to handle that type of data. See the Plugger question for more information.