How does one link facebook to tumblr?

[Christina]

I've searched how to do this (and found a lot of ways it can be done) but none of them are working. I've tried going under the setting on tumblr and hitting "sign in with facebook", but nothing comes up where I can log in. I've also tried searching for the tumblr application on facebook (through this link: apps.facebook.com/tumblr-feed, given by a lot of different help sites) but it just comes up with an error message.

How does one link the two? I am missing something? Thanks!