Had exact same problem 2/12/13 - went to Apple Store and they re-installed iOS on Mac Pro. Restored from Time Capsule and Safari wouldn't work. Your link http://swcdn.apple.com/content/downloads/37/23/041-5058/lr5tynbldi18zcrqo8a8uq88 rnjushqliu/Safari6Lion.pkg worked perfectly.
In fact - I didn't even need to get Firefox. I cut and pasted the link to an email. I opened the email on the affected computer and right-clicked on the link and chose "Download Linked File". It didn't require Safari to actually open, but it did download the patch to the Download folder which then fixed it within a minute. Thank you SO much!