When the first Firefox browser was released, it got a lot of attention very fast. It was obvious that open sourcing the existing code was definitely the right choice. There is also a great documentary available on YouTube, called "Project Code Rush - The Beginnings of Netscape". The documentary basically tells the story about the days when Firefox was about to be released. Changing the code to make it OSS is nothing outdated - its the same thing Microsoft does these days. It actually takes a lot of time and efforts to make an existing code base a representable, functional open-source code.
One might ask what is still to do? Actually a lot. Let's consider the mobile phone market for a second. There are a few really strong operating systems. We have iOS (closed, very popular, but also limited to just a single vendor) and Android (open, even more popular, but exists in many flavors distributed by many vendors). We also have minor players such as Windows Phone (closed, but uniform and with many vendors) and Blackberry (same as for iOS). Every OS has their own UI framework (of course!), and requires their own programming language (at least out-of-the-box). This is a lot of commitment for a single platform.
Such an OS also requires more research to optimize performance. Therefore Mozilla not only created a great project called "Servo", which is a next generation browser engine, but also a new programming language called "Rust". Rust is just awesome. It basically tries to be a possible successor to C++, which drops a lot of legacy features and focuses on reliability. The language also comes with a way of distributing packages, referencing them or managing them.
I did not mention projects such as Emscripten (which is using LVVM), Shumway or broadway.js. Nevertheless, I guess the few paragraphs above indicate that Mozilla is doing a lot for advancing the web. This is an ongoing revolution and we already see parts of it being used in other great projects or products.
Hence I want to conclude with a big thank you to the Mozilla Foundation. You're doing great work!