Downloaded 4.o from website to replace my 3.x on my PowerPC G4 Mac. It offered an icon to move into Applications folder that had a circle with slashing line across it. I (perhaps foolishly) moved that to Applications folder, which wiped out 3.x version. Now, this new but not working Firefox file gives an "Application Not Supported" warning when I try to open it. Thus, no Firefox, and retrying download didn't help.