What font does Mozilla use?

Mozilla ran its 2017 identity work in public, which is rare enough to be worth the page on its own: the routes not taken were posted as they were argued about. What came out of it was a wordmark that spells the name with a URL path in the middle of it, and a slab serif to set it in.

Zilla Slab was drawn by Typotheque and is an open font, so it is on this site and on your machine if you want it. It is a slab in the sense that matters — the serifs are squared off and carry the same weight as the stems — but the shapes underneath are closer to a humanist sans than to the nineteenth-century slabs the category is named after, which is why it reads as friendly rather than as a wanted poster.

Firefox itself is a slightly different question. The browser’s product identity uses Mozilla’s house family, but the fox is an illustration and the wordmark alongside it has been redrawn more than once. If you are looking for the face, it is Zilla Slab; if you are looking for the logo, that is artwork.