Type "mount". If the list of options after "/dev/disk0s3 on /" does not include "read-only", that's your problem. I'm pretty sure you really need to boot into single-user mode in order to do this. And I assume safe-mode isn't single-user mode, as, IIRC, single-user mode puts you at a CLI-only interface and I doubt there's a CLI web browser available. Or network access, for that matter.

If you have another Mac available, you might be able to do it by booting into Firewire target mode and doing an fsck from that machine. The device will be different. You'll probably have to umount the filesystem once MacOS mounts it automatically for you.

If it is already mounted read-only, let us know and we can try to figure out what your alternate superblocks might be, but I don't want to head down that path unless we're sure we need to.