I'm probably not legally allowed to redistribute these (you pay good money for those fonts!), so you'll have to download them yourself.

You can get the up-to-date links by loading up a tumblr post (here's a good one: https://www.tumblr.com/knuxify/722271667278233600/ignore-me-im-a-formatting-test), opening your browser's dev tools, going to the network tab, ticking "Disable Cache", refreshing the page, then sorting by the "type" column and scrolling down to find all the woff2 fonts.

fxtumblr looks for the following fonts:

• favorit-85.woff2
• favorit-85-italic.woff2
• favorit-medium.woff2
• fairwater-regular.woff2

Download them and place them in this directory. fxtumblr should be able to find them automatically.