Alright, the description wasn't very good... Assume you have a frameset, with frames A B and C... Frame B is another frameset, with frames B1, B2, and B3. If a link in any of the Bx frames attempts to target frames A, or C, it will freeze the browser. It looks like links can only target frames paralell to them safely. While it may not be HTML compliant to target other/parent framesets, it should be made safe to click on, at least. In the URL given, this is the case. Three vertical frames (A,B,C), and three horizontal ones (in the middle; 1,2,3)... if you click on any of the lower set of links (which target B), it'll freeze mozilla... (Nov 5, 2000)
I can't reproduce with URL provided. I would need a simplified test case provided by the reporter.
Seems to work in latest build... all is well.
Marking verified per last comments