Netscape 6 support Mac OS 8.6 and later, however regarding Mac OS X, the netscape installation notes state the following:
We are offering Netscape 6.1 for Mac OS X as a Preview Release. Preview Release software is software that is not in its final form. We are interested in getting feedback and suggestions from advanced end-users or testers to help solidify the final product. Your support of this program is greatly appreciated but no technical support is offered. If you are using Netscape 6 as your current browser, install this version of Netscape 6.1 to a different directory. Installing Netscape 6.1 should not interfere with Netscape software prior to Netscape 6 or other browsers. As with any preview release, back up your system prior to installation. Any feedback is through the netscape address given in my previous answer, good luck with it.