try with software FPU

http://www.umich.edu/~archive/mac/system.extensions/cdev/softwarefpu3.03.sit.hqx

this kind of errors usally come when you run a 68k app on PowerPC, because the Mac OS emulate the 68020 code without the floating point coprocessor ... in your case ... I do not know maybe bugy netscape written in FAT code