A Quantum Leap for the Web

David Bryant
Mozilla Tech
Published in
4 min readOct 27, 2016


Over the past year, our top priority for Firefox was the Electrolysis project to deliver a multi-process browsing experience to users. Running Firefox in multiple processes greatly improves security and performance. This is the largest change we’ve ever made to Firefox, and we’ll be rolling out the first stage of Electrolysis to 100% of Firefox desktop users over the next few months.

But, that doesn’t mean we’re all out of ideas in terms of how to improve performance and security. In fact, Electrolysis has just set us up to do something we think will be really big.

We’re calling it Project Quantum.

Quantum is our effort to develop Mozilla’s next-generation web engine and start delivering major improvements to users by the end of 2017. If you’re unfamiliar with the concept of a web engine, it’s the core of the browser that runs all the content you receive as you browse the web. Quantum is all about making extensive use of parallelism and fully exploiting modern hardware. Quantum has a number of components, including several adopted from the Servo project.

The resulting engine will power a fast and smooth user experience on both mobile and desktop operating systems — creating a “quantum leap” in performance. What does that mean? We are striving for performance gains from Quantum that will be so noticeable that your entire web experience will feel different. Pages will load faster, and scrolling will be silky smooth. Animations and interactive apps will respond instantly, and be able to handle more intensive content while holding consistent frame rates. And the content most important to you will automatically get the highest priority, focusing processing power where you need it the most.

So how will we achieve all this?

Web browsers first appeared in the era of desktop PCs. Those early computers only had single-core CPUs that could only process commands in a single stream, so they truly could only do one thing at a time. Even today, in most browsers an individual web page runs primarily on a single thread on a single core.

But nowadays we browse the web on phones, tablets, and laptops that have much more sophisticated processors, often with two, four or even more cores. Additionally, it’s now commonplace for devices to incorporate one or more high-performance GPUs that can accelerate rendering and other kinds of computations.

One other big thing that has changed over the past fifteen years is that the web has evolved from a collection of hyperlinked static documents to a constellation of rich, interactive apps. Developers want to build, and consumers expect, experiences with zero latency, rich animations, and real-time interactivity. To make this possible we need a web platform that allows developers to tap into the full power of the underlying device, without having to agonize about the complexities that come with parallelism and specialized hardware.

And so, Project Quantum is about developing a next-generation engine that will meet the demands of tomorrow’s web by taking full advantage of all the processing power in your modern devices. Quantum starts from Gecko, and replaces major engine components that will benefit most from parallelization, or from offloading to the GPU. One key part of our strategy is to incorporate groundbreaking components of Servo, an independent, community-based web engine sponsored by Mozilla. Initially, Quantum will share a couple of components with Servo, but as the projects evolve we will experiment with adopting even more.

A number of the Quantum components are written in Rust. If you’re not familiar with Rust, it’s a systems programming language that runs blazing fast, while simplifying development of parallel programs by guaranteeing thread and memory safety. In most cases, Rust code won’t even compile unless it is safe.

We’re taking on a lot of separate but related initiatives as part of Quantum, and we’re revisiting many old assumptions and implementations. The high-level approach is to rethink many fundamental aspects of how a browser engine works. We’ll be re-engineering foundational building blocks, like how we apply CSS styles, how we execute DOM operations, and how we render graphics to your screen.

Quantum is an ambitious project, but users won’t have to wait long to start seeing improvements roll out. We’re going to ship major improvements next year, and we’ll iterate from there. A first version of our new engine will ship on Android, Windows, Mac, and Linux. Someday we hope to offer this new engine for iOS, too.

We’re confident Quantum will deliver significantly improved performance. If you’re a developer and you’d like to get involved, you can learn more about Quantum on the the Mozilla wiki, and explore ways that you can contribute. We hope you’ll take the Quantum leap with us.

Special thanks to Ryan Pollock for contributing to this post.



David Bryant
Mozilla Tech

Mozilla Fellow, lifelong engineer and builder of things. Spent time at Bell Labs, Sun Microsystems, and Nokia.