Which is apparently compatible with Mountain Lion.
For the record, my upgrade to Lion was a complete pain in the ass: my external backup drive wasn't compatible and Lion ate the partition. So had I taken the common advice and backed up before a complete wipe I would have lost everything in the upgrade.
If you're not up for that sort of pain, just switch to Chrome. It's a much better browser than Safari and you'll get updates for it whether Apple wants you to or not.