This month in Servo: color inputs, SVG, embedder JS, and more!

Two big pieces of news for images in Servo this month:

1. We now display animated GIFs in all their animated glory (@rayguo17, #36286)! This work required careful architecting to integrate with existing animation mechanisms in the engine without incurring unnecessary CPU usage.

2. We support loading SVG images in <img src> (@mukilan, @mrobinson, #36721).

Outreachy

We’re excited to host two Outreachy interns over the next few months! Jerens Lensun (@jerensl) will be working on improving Servo’s CI setup and other Python-focused infrastructure, while Usman Baba Yahaya (@uthmaniv) will implement support for the Network Monitor in our devtools.

They will both be blogging about their internships, and you can follow their work on Jeren’s blog and Usman’s blog.

Web content

Servo’s layout implementation has historically been all-or-nothing — any change in the page, no matter how isolated, requires laying out the entire page from scratch. Fixing this limitation is known as incremental layout, and it’s a key performance optimization in all browser engines. This month we’ve landed a number of changes in this area that make some kinds of CSS changes much more efficient than a full layout (@mrobinson, @Loirooriol, #36896, #36978, #37004, #37047, #37069, #37048, #37088, #37099).

We have also made significant progress on the Trusted Types API, going from 47% of tests passing to 58% over the course of May (@TimvdLippe, #36710, #36668, #36811, #36824, #36941, #36960). Supporting this work on Trusted Types, our Content Security Policy implementation has been steadily improving, now passing 59% of automated tests (@TimvdLippe, @jdm, @simonwuelker, #36709, #36710, #36776, #36832, #36860, #36887, #36923, #36963, #36962, #36961, #36965, #37020).

We’ve enabled support for URLPattern (@simonwuelker, #36826, #37004, #37116), <input type=color> (@simonwuelker, #36992), plus several other web API features:

• TransformStream (@Taym95, @gterzian, #36739, #36905)
• setHTMLUnsafe() method on ShadowRoot (@TG199, #36240)
• scrollingElement property on Document (@JimmyDdotEXE, #35994)
• pipeThrough() method on ReadableStream (@Taym95, #36977)
• readText() method on navigator.clipboard (@Gae24, #36689)
• type property on Stylesheet (@simonwuelker, #37126)

Our layout and CSS support continues to improve. This month, we improved our page background sizing and style computation (@mrobinson, @Loirooriol, #36917, #37147), and added support for ‘wavy’ and ‘double’ in the ‘text-decoration-line’ property (@mrobinson, #37079).

HTMLVideoElement can now be used as an image source for 2D canvas APIs (@tharkum, #37135), ImageBitmap can be serialized and transferred via postMessage() (@tharkum, #37101), media elements redraw properly whenever their size changes (@tharkum, #37056), polygon image map areas are clickable (@arihant2math, #37064), <select> elements are redrawn when their contents change (@simonwuelker, #36958), and getPreferredCanvasFormat() on GPU returns platform-appropriate values (@arihant2math, #37073).

We’ve fixed bugs relating to invertible and non-invertible transforms (@Loirooriol, #36749, #37147), missing underlines on macOS (@mrobinson, #37029), and sizing issues for tables and flex containers (@stevennovaryo, @Loirooriol, #36703, #36993, #36980, #37024, #37011). We’ve also fixed a number of bugs where Servo’s behaviour did not match relevant specifications:

• input events are now fired following keydown events (@yezhizhen, #37078)
• unscopable objects are now writable and readable, and don’t have a prototype (@simonwuelker, #37119, #37122)
• Request headers reject more erroneous headers (@sebsebmc, #36943)
• External stylesheets in documents with quirks mode are more lenient about the stylesheet’s Content-Type (@ghostd, @mrobinson, #28321)
• the ImageData constructor throws better errors for unsupported arguments (@Taym95, #31398)
• Attribute nodes are serialized as the empty string (@simonwuelker, #36875)
• custom element is values are serialized as attributes (@simonwuelker, #36888)
• EventSource ignores invalid field values and treats non-200 responses codes as failures (@KiChjang, #36853, #36854)
• the premultipliedAlpha flag for WebGL canvases premultiplies correctly (@tharkum, #36895)

Our WebDriver server implementation received a lot of attention this month! Element clicks now receive the expected button value (@longvatrong111, #36871), wheel actions are supported (@PotatoCP, #36744, #36985), and we removed the possibility of races between some input actions and other WebDriver commands (@longvatrong111, @mrobinson, #36932). We’ve also added support for passing WebDriver references to DOM objects as arguments when executing scripts (@jdm, #36673), and fixed some bugs with JS value serialization (@yezhizhen, #36908) and cancelling inputs (@yezhizhen, #37010).

We’ve begun preparatory work to integrate Vello as the backend for 2D canvases (@sagudev, #36783, #36790, #36999). We’ve also landed some changes towards supporting ‘::placeholder’ pseudo-elements and fixing rendering issues with text inputs (@stevennovaryo, #37065).

Embedding

The engine

Embedders can now evaluate JavaScript inside a webview and receive results asynchronously (@Narfinger, @mrobinson, #35720).

All embedders will receive default styling and interactivity for elements like inputs and media elements (@webbeef, #36803), reducing the amount of configuration required to embed the engine.

Any provided system light/dark theme will be propagated to all documents loaded inside of a webview (@mrobinson, #37132).

Servo’s developer tools integration now highlights elements in the layout inspector (@simonwuelker, #35822), and displays <!DOCTYPE> nodes correctly (@simonwuelker, #36787).

We have removed the dom_shadowdom_enabled preference, since the feature has been enabled by default since March 2025 (@simonwuelker, #37043).

Our automated benchmarking setup is expanding, and we can now measure how long it takes to start up Servo and load the servo.org homepage on HarmonyOS (@Narfinger, #36878), which will help us identify regressions in the future.

Finally, we can now write unit tests for Servo’s embedding API (@mrobinson, #36791), which allows us to write better regression tests for shutdown-related issues (@mrobinson, #36808).

servoshell

The --user-agent (-u) flag now correctly sets the User-Agent header for network requests (@PartiallyUntyped, @mrobinson, #36859).

Service workers have been removed from the list of features enabled by --enable-experimental-web-platform-features until they provide more value (@jdm, #36867).

Building servoshell with --with-asan now causes all C++ dependencies to be built with Address Sanitizer as well, and mach bootstrap on Windows can now use winget as a fallback if choco is unavailable (@jschwe, #32836).

The current system light/dark theme is now queried on startup (@Legend-Master, #37128). Additionally, the screen dimensions and geometry reported by the engine are now correct on OpenHarmony (@PartiallyUntyped, @jschwe, #36915).

Performance

Servo is now better at evicting image data from GPU caches (@webbeef, #36956). We also reduced the memory needed to store HSTS data, saving more than 60mb by doing so (@sebsebmc, #37000, #37015).

We now measure the memory usage of sessionStorage and localStorage data (@jdm, #37053), the Public Suffix List (@sebsebmc, #37049), and system fonts (@jdm, #36834).

In addition, we’ve reduced the size of the final Servo binary by 2 MB by stripping out DOM code that should never be used outside of automated tests (@jdm, #37034).

Stability

We fixed a number of crashes involving animated images (@simonwuelker, #37058), media elements with an unknown duration (@tharkum, servo-media#437), canvas elements during shutdown (@mrobinson, #37182), adding a Path2D to itself (@Taym95, #36847), calculating IntersectionObserver areas (@webbeef, #36955), the childNodes() method on Node (@jdm, #36889), resizing OffscreenCanvas (@simonwuelker, #36855), querying WebGL extensions (@mrobinson, #36911), and slicing a sliced Blob (@simonwuelker, #36866).

We’ve also fixed a deadlock involving streams with very large chunks (@wusyong, #36914), and fixed a source of intermittent crashes when closing tabs or removing iframes (@jdm, #37120). Finally, we rewrote the implementation of the text property on HTMLOptionElement to avoid crashes with deeply-nested elements (@kkoyung, #37167).

Having previously noticed an unsafe pattern triggered by using JS-owned values in Rust Drop implementations (#26488), we have begun incrementally removing existing Drop impls to remove that source of unsafety (@willypuzzle, #37136).

Upgrades

We upgraded our fork of WebRender to April 2025 (@mrobinson, #36770), and upgraded our Stylo dependency to May 2025 (@Loirooriol, #36835). These changes ensure that Servo is up to date with ongoing work in Firefox, which shares these dependencies.

Donations

Thanks again for your generous support! We are now receiving 4597 USD/month (−1.4% over April) in recurring donations. This helps cover the cost of our self-hosted CI runners and one of our latest Outreachy interns!

Servo is also on thanks.dev, and already 25 GitHub users (+1 over April) that depend on Servo are sponsoring us there. If you use Servo libraries like url, html5ever, selectors, or cssparser, signing up for thanks.dev could be a good way for you (or your employer) to give back to the community.

4597 USD/month

10000

As always, use of these funds will be decided transparently in the Technical Steering Committee. For more details, head to our Sponsorship page.