Mozilla’s latest Firefox release, version 83.0, boosts a major increase to JavaScript performance.

JavaScript, once mainly used for animations and menus, is one of the most important languages of the web. Thanks to JavaScript, developers are able to create complex web applications, many of which rival desktop applications for functionality.

Unfortunately, running JavaScript-heavy websites is one of the most challenging aspects of a web browser’s duties. Every major browser manufacturer constantly works to increase JavaScript performance and responsiveness.

Mozilla’s latest version of Firefox significantly boosts the browser’s performance thanks to a major update to its SpiderMonkey JavaScript engine. The new update, called Warp or WarpBuilder, makes changes to the Just-In-Time (JIT) compilers.

With Warp (also called WarpBuilder) we’re making big changes to our JIT (just-in-time) compilers, resulting in improved responsiveness, faster page loads and better memory usage. The new architecture is also more maintainable and unlocks additional SpiderMonkey improvements.

Traditionally, JavaScript is an interpreted language. That means the code is interpreted on the fly as it is executed. This can result in major performance issues, especially when code must be executed repeatedly, such as code loops. JIT compilers help solve this problem by compiling and storing frequently used code, speeding up operations.

Firefox’s latest boost comes from significantly optimizing those JIT compilers, resulting in significant real-world gains over Warp’s predecessor Ion.

Warp is faster than Ion on many workloads. The picture below shows a couple examples: we had a 20% improvement on Google Docs load time, and we are about 10-12% faster on the Speedometer benchmark.

We’ve seen similar page load and responsiveness improvements on other JS-intensive websites such as Reddit and Netflix. Feedback from Nightly users has been positive as well.

Although Firefox is no longer the leading browser, in terms of market share, it continues to be a major player. Its improved performance, not to mention emphasis on privacy, will hopefully help it gain some ground against its larger rivals.