Firefox is written in rust, millions of users indeed. But to answer your question, no, I wish I could deploy something written in rust to production. I don’t think there is a problem with the language, just a risk of not being able to find developers to support it. I think a lot of companies are on the sidelines about it still. Given that it’s a difficult language to learn there may be some fear in that area about its future.

Cloudflare uses it in prod: https://news.ycombinator.com/item?id=17077358

Here's a list of companies: https://www.rust-lang.org/friends.html