The idea is that Rust is to Firefox what C is to Unix. It is a general purpose language, but one that is specifically designed to address the kind of problem you have when writing a web browser.

It was a Mozilla side project, but with Servo, totally in line with its mission of making a good web browser. I'd even say it was a necessary long term plan. Chrome was the better, more modern browser, and Firefox needed fundamental improvements like these to compete. If anything, I think they should have spent more energy on Rust and Servo, not less.

> Software developer Graydon Hoare created Rust as a personal project while working at Mozilla Research in 2006. Mozilla officially sponsored the project in 2009

According to https://en.wikipedia.org/wiki/Rust_(programming_language)

Rust is different though, because its purpose was to make Firefox more secure. So the ultimate goal was to improve the browser. Maybe there is some way this acquisition leads to a better browser, but I don't see it.