This Month in Ladybird: March 2025
March 2025 is all wrapped up, and it's been another solid month for the Ladybird project. We’ve merged 285 PRs from 47 contributors and made progress on all fronts.
Welcoming new sponsors
Ladybird is entirely funded by the generous support of companies and individuals who believe in the open web. This month, we're excited to welcome the following new sponsors:
- ohne-makler.net (renewing) with $50,000
- Sourcegraph with $5,000
- Travis Heinström with $1,000
We are incredibly grateful for their support. If you're interested in sponsoring the project, please contact us.
Web Platform Tests (WPT)
Although we've exhausted the low-hanging fruit, we nevertheless continue to improve our WPT score by fixing engine bugs and implementing more features.
This month, we have 8,249 new passing tests, bringing the total to 1,782,048.
It's also noteworthy that Safari overtook Firefox this month.
Video improvements + very basic YouTube support
Last year, we began using FFmpeg to decode videos, which gave us access to a lot more formats than just VP9. However, we didn't use FFmpeg to demux video containers, instead keeping our home-grown Matroska implementation. This meant we could only play H.264 videos if they were in an MKV container file.
This month, we've replaced our Matroska demuxer with FFmpeg's libavformat demuxer. This lets us handle all containers supported by FFmpeg, such as the very popular MP4.
If we don't advertise support for ManagedMediaSource, we can even play 360p H.264 fallback videos on YouTube!
Try playing the above MP4 videos in Ladybird :^)
Site isolation (AKA process per origin)
Site isolation is an important security feature in modern browsers, ensuring that two different websites never share the same OS process. This helps prevent malicious websites from accessing your data on other websites. We've started implementing this feature in Ladybird, and although it's not yet complete, it's a crucial step toward protecting users.
Settings UI overhaul
We've begun implementing a unified settings page for Ladybird, available now at about:settings. This will allow us to
centralize all Ladybird settings in a single interface, providing a common experience across all platforms.
background-blend-mode
We've implemented the background-blend-mode property, which lets authors apply different blending modes to their
backgrounds for a variety of visual effects.
Firefox DevTools, continued
Last month, we started implementing the Firefox DevTools protocol, making it possible to use Firefox's developer tools with Ladybird. This month, we've added the ability to inspect style sheets and fonts, and expanded our integration with the JavaScript console. We also added support for performing live edits of web elements directly from DevTools.
We have now implemented enough of the protocol that we were able to remove our home-grown tooling. As a result, we now rely entirely on DevTools!
Caching intrinsic sizes for faster relayout
In CSS, "intrinsic sizes" (simplified) are the sizes an element would occupy in each axis if it were given either minimal or limitless available space.
Unlike normal layout metrics which often change due to context differences, intrinsic sizes tend to remain the exact same between relayouts. Given this, we now strive to aggressively cache intrinsic sizes. This significantly reduces the amount of work done by each relayout.
Moving rasterization into separate thread
Over a year ago, we introduced display lists that represent an immutable, serialized sequence of painting commands. This month, we finally took advantage of that architecture by moving rasterization of display lists off the main thread. As a result, the main thread now has more time to handle other tasks like layout, JavaScript execution, and garbage collection.
New @supports features
We now support the font-format() and font-tech() functions inside @supports rules, which allow authors to choose
what CSS to apply based on our font support.
Also, we fixed a couple of bugs with @supports selector(), making it work more reliably.
Behind the scenes, @media and @supports now share the same code for parsing and evaluating a boolean expression.
This makes them easier to maintain, and prepares us for future CSS features such as @when.
Pseudo-element improvements
This month, we started generating much of our pseudo-element code from JSON at compile time, like we do for pseudo-classes. This makes it simpler to add new ones, and also makes it easier to add a few new features such as aliases, and limiting which properties can be applied to different pseudo-elements.
This has allowed us to replace our ::-webkit-* pseudo-elements, which we implemented in the past for a few form
widgets, with ones based on the new CSS Forms spec, while still supporting sites that use the -webkit-* or -moz-*
versions.
We also have support for function pseudo-elements, for example ::foo(bar), which are being used more and more in
recent CSS features.
Team workshop
A bunch of us got together in London this month and spent a week working on Ladybird in a small kitchen. Here's what it looked like, filtered through OpenAI's new 4o image generation tool, which launched this week (and which we quickly got working in Ladybird):
Throughout the week we were dogfooding the Uber Eats website, using it as our primary way of ordering food while actively hunting down bugs.
A lot of little quirks and major blocking issues were fixed to the point where we were successfully able to find a restaurant, order the food, pay for it and even track the order to our doorstep!
Ladybird roadshow
We presented Ladybird at two conferences this month:
Don't Be Evil at FUTO in Austin, TX:
State of the Browser in London, UK:
Both talks were very well-received and there was palpable excitement about our work. Big thanks to the organizers and everyone who came out to hear about Ladybird in person!
Credits
We'd like to thank everyone who contributed code this month:
Alec Murphy, Ali Mohammad Pur, Aliaksandr Kalenik, Andreas Kling, Andrew Kaster, Feng Yu, Gingeh, Glenn Skrzypczak, InvalidUsernameException, Jelle Raaijmakers, Jess, Kevin Mas Ruiz, Lucas CHOLLET, Lucien Fiorini, Lukas Scheller, Luke Wilde, Manuel Zahariev, Mehran Kamal, Noah, NotAShelf, Oliver Medhurst, Piotr Bartoszewicz, Psychpsyo, R-Goc, Rok Povsic, Ryan Liptak, SINF-KEN, Sam Atkins, Shannon Booth, Tim Ledbetter, Timothy Flynn, Tommy van der Vorst, Totto16, Vaxry, Vishal Biswas, Yaroslav Lelkin, aplefull, devgianlu, mikiubo, rmg-x, sideshowbarker, stasoid, stelar7