Stylo shipped a long time ago now, in Firefox 57. https://wiki.mozilla.org/Oxidation#Rust_Components https://wiki.mozilla.org/Oxidation#Rust_Components has a l

Stylo shipped a long time ago now, in Firefox 57. https://wiki.mozilla.org/Oxidation#Rust_Components https://wiki.mozilla.org/Oxidation#Rust_Components has a list of what Rust has shipped within Firefox, though most of it has been motivated by safety guarantees rather than parallelism.