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Firefox’s crash reporter is hopefully not something that most users experience often. However, it is still a very important component of Firefox, as it is integral in providing insight into the most visible bugs: those which crash the main process. These bugs offer the worst user experience (since the entire application must close), so fixing them is a very high priority. Other types of crashes, s

One of the biggest challenges for any software is to determine how changes impact user experience in the real world. Whether it’s the processing speed of video editing software or the smoothness of a browsing experience, there’s only so much you can tell from testing in a controlled lab environment. While local experiments can provide plenty of metrics, improvements to those metrics may not transl

The first computer I owned shipped with 128 KiB of RAM and to this day I’m still jarred by the idea that applications can run out of memory given that even 15-year-old machines often shipped with 4 GiB of memory. And yet it’s one of the most common causes of instability experienced by users and in the case of Firefox the biggest source of crashes on Windows. As such, at Mozilla, we spend significa

If you’re running Firefox on macOS you might have noticed that its responsiveness has improved significantly in version 103, especially if you’ve got a lot of tabs, or when your machine is busy running other applications at the same time. This improvement was achieved via a small change in how locking is implemented within Firefox’s memory allocator. Firefox uses a highly customized version of the

In June 2021, we decided to start converting the source code for MDN web docs from HTML into a format that would be easier for us to work with. The goal was to get 100% of our manually-written documentation converted to Markdown, and we really had a mountain of source code to climb for this particular expedition. In this post, we’ll describe why we decided to migrate to Markdown, and the steps you

Merging two GitHub repositories without losing commit history We are in the process of merging smaller example code repositories into larger parent repositories on the MDN Web Docs project. While we thought that copying the files from one repository into the new one would lose commit history, we felt that this might be an OK strategy. After all, we are not deleting the old repository but archiving

Ecma International recently approved the 2022 standard of ECMAScript. There is something new in this edition that hasn’t been part of prior editions, but this isn’t a new programming feature. In March of this year, Ecma International accepted a proposal led by Mozilla for a new alternative license. On June 22nd, the first requests to adopt this license were granted to TC39 and applied to the follo

This is part 2 of a series of articles on rust-minidump. For part 1, see here. So to recap, we rewrote breakpad’s minidump processor in Rust, wrote a ton of tests, and deployed to production without any issues. We killed it, perfect job. And we still got massively dunked on by the fuzzer. Just absolutely destroyed. I was starting to pivot off of rust-minidump work because I needed a bit of palette

In Firefox 98, we’re shipping a new version of the existing Performance panel. This panel is now based on the Firefox profiler tool that can be used to capture a performance profile for a web page, inspect visualized performance data and analyze it to identify slow areas. The icing on the cake of this already extremely powerful tool is that you can upload collected profile data with a single click

MDN is one of the most trusted resources for information about web standards, code samples, tools, and everything you need as a developer to create websites. In 2015, we explored how we could expand beyond documentation to provide a structured learning experience. Our first foray was the Learning Area, with the goal of providing a useful addition to the regular MDN reference and guide material. In

Chrome and Firefox will reach version 100 in a couple of months. This has the potential to cause breakage on sites that rely on identifying the browser version to perform business logic.  This post covers the timeline of events, the strategies that Chrome and Firefox are taking to mitigate the impact, and how you can help. User-Agent string User-Agent (UA) is a string that browsers send in HTTP he

Retrospective and Technical Details on the recent Firefox Outage On January 13th 2022, Firefox became unusable for close to two hours for users worldwide. This incident interrupted many people’s workflow. This post highlights the complex series of events and circumstances that, together, triggered a bug deep in the networking code of Firefox. What Happened? Firefox has a number of servers and rela

WebAssembly and Back Again: Fine-Grained Sandboxing in Firefox 95 In Firefox 95, we’re shipping a novel sandboxing technology called RLBox — developed in collaboration with researchers at the University of California San Diego and the University of Texas — that makes it easy and efficient to isolate subcomponents to make the browser more secure. This technology opens up new opportunities beyond wh

Firefox 93 comes with lots of lovely updates including AVIF image format support, filling of XFA-based forms in its PDF viewer and protection against insecure downloads by blocking downloads relying on insecure connections. Web developers are now able to use static initialization blocks within JavaScript classes, and there are some Shadow DOM and Custom Elements updates. The SHA-256 algorithm is n

Starting with Firefox 93, Firefox will monitor available system memory and, should it ever become so critically low that a crash is imminent, Firefox will respond by unloading memory-heavy but not actively used tabs. This feature is currently enabled on Windows and will be deployed later for macOS and Linux as well. When a tab is unloaded, the tab remains in the tab bar and will be automatically r

Last month, Gregor Weber and I added an autocomplete search to MDN Web Docs, that allows you to quickly jump straight to the document you’re looking for by typing parts of the document title. This is the story about how that’s implemented. If you stick around to the end, I’ll share an “easter egg” feature that, once you’ve learned it, will make you look really cool at dinner parties. Or, perhaps y

This post is cross-posted from Matthew Gaudet’s blog When implementing a language feature for JavaScript, an implementer must make decisions about how the language in the specification maps to the implementation. Sometimes this is fairly simple, where the specification and implementation can share much of the same terminology and algorithms. Other times, pressures in the implementation make it mor

While we’re sitting here feeling a bit frumpy after a year with reduced activity, Firefox 89 has smartened up and brings with it a slimmed down, slightly more minimalist interface. Along with this new look, we get some great styling features including a force-colors feature for media queries and better control over how fonts are displayed. The long awaited top-level await keyword for JavaScript mo

Roughly a year ago at Mozilla we started an effort to improve Firefox stability on Linux. This effort quickly became an example of good synergies between FOSS projects. Every time Firefox crashes, the user can send us a crash report which we use to analyze the problem and hopefully fix it: This report contains, among other things, a minidump: a small snapshot of the process memory at the time it c

Introducing Firefox’s new Site Isolation Security Architecture Like any web browser, Firefox loads code from untrusted and potentially hostile websites and runs it on your computer. To protect you against new types of attacks from malicious sites and to meet the security principles of Mozilla, we set out to redesign Firefox on desktop. Site Isolation builds upon a new security architecture that ex

tl;dr: Support for QUIC and HTTP/3 is now enabled by default in Firefox Nightly and Firefox Beta. We are planning to start rollout on the release in Firefox Stable Release 88. HTTP/3 will be available by default by the end of May. What is HTTP/3? HTTP/3 is a new version of HTTP (the protocol that powers the Web) that is based on QUIC. HTTP/3 has three main performance improvements over HTTP/2: Bec

State Partitioning is the technical term for a new privacy feature in Firefox called Total Cookie Protection, which will be available in ETP Strict Mode in Firefox 86. This article shows how State Partitioning works inside of Firefox and explains what developers of third-party integrations can do to stay compatible with the latest changes. Web sites utilize a variety of different APIs to store dat

To wrap up January, we are proud to bring you the release of Firefox 85. In this version we are bringing you support for the :focus-visible pseudo-class in CSS and associated devtools, <link rel="preload">, and the complete removal of Flash support from Firefox. We’d also like to invite you to preview two exciting new JavaScript features in the current Firefox Nightly — top-level await and relativ

Improving Cross-Browser Testing, Part 1: Web Application Testing Today Testing web applications can be a challenge. Unlike most other kinds of software, they run across a multitude of platforms and devices. They have to be robust regardless of form factor or choice of browser. We know this is a problem developers feel: when the MDN Developer Needs Assessment asked web developers for their top pain

As December ushers in the final curtain for this rather eventful year, there is time left for one more Firefox version to be given its wings. Firefox 84 includes some interesting new features including tab order inspection, complex selector support in :not(), the PerformancePaintTiming API, and more! This blog post provides merely a set of highlights; for all the details, check out the following: