August in Servo: CSS Grid, text selection, and more!

This release also contains significant improvements to navigation, document loading, and session history, which are some of the gnarliest parts of the HTML specification. Who knew that loading about:blank was so complicated? The upshot to all this work is that pages that open additional windows or include iframes work much more reliably.

This is another big update, so here’s an outline:

• Security
• Real world compat
• Work in progress
• Embedding API
• For users and developers
• More on the web platform
• Performance and stability
• New contributors

Security

We upgraded to SpiderMonkey v153, which brings many new security and crash fixes to Servo’s JavaScript engine integration (@sagudev, @Gae24, #47489).

Navigating away from a document that activated fullscreen mode now exits fullscreen mode (@shubhamg13, @jdm, #47123).

Real world compat

CSS Grid enabled by default means that many websites with traditional grid layouts now look correct, like rustweek.org.

v0.5.0

v0.6.0

2026.rustweek.org

It also makes a lot of websites look better that you wouldn’t assume rely on CSS Grid:

v0.5.0

v0.6.0

labs.jensimmons.com

Panning gestures initiated by touch inputs now lock to the dominant axis (@yezhizhen, #46983). This results in more predictable panning when interacting with pages in Servo.

We fixed a crash affecting gumroad.com.au (@lumiscosity, #47266).

We’re interested to hear how well your favourite websites run in Servo! Report successes in this Zulip thread, and failures in our GitHub issues.

Work in progress

Accessibility support in Servo continues to make great strides; it can be enabled with the --pref accessibility_enabled command line argument. Servo now reports positions and sizes for items in the content accessibility tree (@philocalyst, @alice, @mrobinson, #46996), allowing macOS VoiceOver to work more reliably. We also report many ARIA roles for web content elements to accessibility toolkits (@mukilan, #47318).

Full list of supported roles

• alert
• banner
• blockquote
• caption
• code
• complementary
• contentinfo
• definition
• deletion
• directory
• document
• emphasis
• feed
• figure
• generic
• insertion
• list
• log
• main
• math
• navigation
• none
• note
• paragraph
• presentation
• rowgroup
• search
• status
• strong
• term
• time
• timer

Servo’s support for Document.execCommand() is rapidly improving, and can be enabled with --pref dom_exec_command_enabled. We fixed issues with the inserttext command (@Psychpsyo, #47224, #47306), editing uneditable content (@Psychpsyo, #47362), computing contained nodes (@TimvdLippe, #47429), adjusting selections in contenteditable (@mrobinson, #47393, #47581, #47581), and implemented the indent and insertLineBreak commands (@Psychpsyo, #47416, #47445).

We made a lot of progress on the LargestContentfulPaint performance metric, implemented behind the --pref largest_contentful_paint_enabled argument. Servo now supports the element and loadTime attributes, (@shubhamg13, #46553, #47475), URLs for video element posters (@shubhamg13, #43376), accurate size information (@shubhamg13, #43378), and painting text nodes (@shubhamg13, #47212).

There was preparatory work for a future AudioWorklet implementation (@niyabits, #46856, #47016, #47199). See Niya’s blog post about her Outreachy project for more details!

We’re continuing work on the ServiceWorker feature, which can be enabled with --pref dom_serviceworker_enabled. This month we implemented the CookieStore interface behind the --pref dom_cookiestore_enabled command line argument (@Taym95, #47044) as well as the Cache interface (@gterzian, #47220).

Servo now supports a disk-backed HTTP cache that can be enabled with --pref network_http_disk_cache (@Narfinger, #43819). This cache persists between runs, but there is not yet any way to clear it.

Embedding API

Breaking change: WebView::toggle_sampling_profiler has been removed (@lumiscosity, #47014). To perform sampling profiling on Servo, follow the instructions in the book.

Breaking change: The variants of MouseButton have been renamed to Primary, Secondary, and Auxiliary (@mrobinson, @SimonSapin, #47327).

We’ve added several new Cargo features reflecting common usage patterns:

• default_web_features, to include optional web platform features in the build (e.g. WebXR and WebGPU) (@jschwe, #44032)
• bundled, to include required resources in the binary (@jschwe, #44032)
• brotli-compression-stream, enabling support for brotli content in the CompressionStream/DecompressionStream web APIs (@Narfinger, @jdm, #47197)
• webcrypto, to enable support for the Crypto and WebCrypto web APIs (@Narfinger, #47198)
• webgl, to enable support for WebGL (@janeoa, #47200)

For users and developers

One visible change is that interactive text selection now works! This is the result of lots of work across our script and layout code to ensure it respects the actual geometry of the page content (@mrobinson, @SimonSapin, #47022, #47025, #47329, #47358, #46982, #47425, #47438, #47437, #47581, #47070, #47048, #46963).

Building Servo now requires at least Clang 19 on all platforms (@jschwe, #47421). Additionally, the cargo-ohos tool is now required for building for OpenHarmony (@jschwe, #47334).

Debug builds on Windows can now complete successfully (@jschwe, #47372).

Linux arm64 builds have been customized to work on Raspberry Pi 5 (@mukilan, #47113). Any libservo embedders targeting the same platform will require a similar change if they are using jemalloc.

servoshell

Under Wayland and OpenHarmony, we now integrate with the system clipboard (@TheZoq2, @yezhizhen, @jschwe, #46938, #47177).

The macOS command key and Windows logo key is now reported as Meta instead of Super (@eachra-bawn, #47330).

The Android port has had many rough edges filed off as part of modernizing it for the Compose UI (@veyndan, #47656, #47491, #47494, #47697, #46955, #47644, #47652, #47276, #47277, #47299, #47439) and converting its implementation to Kotlin (@veyndan, #46926, #46925, #46951, #46965). Library consumers are no longer responsible for implementing pause and resume support (@veyndan, #47555).

Meanwhile, the OpenHarmony port now supports external keyboards with US keyboard layouts (@jschwe, #47359). Additionally, there are now better fallback font selections for CJK characters (@RichardTjokroutomo, #47116, #47664).

Setting the device_pixel_ratio_override preference is no longer ignored on Android and OpenHarmony (@jschwe, #47081).

Performance and stability

There were many small changes this month that removed unnecessary allocations (@Narfinger, @jschwe, @yezhizhen, #47264, #47147, #47066, #47249, #47249, #47285, #47307, #47343, #47361, #47395, #47427, #47454, #47474, #47506, #47479, #47530, #47541, #47566, #47509, #47622).

We also reduced GC interactions leading to better JS performance (@jdm, @Narfinger, @webbeef, @TimvdLippe, @mrobinson, #47513, #47250, #47158, #47165, #47049, #47251, #47510, #46981).

On platforms that memory map font data (such as OpenHarmony and macOS), we can now save time that would otherwise be spent loading font files from disk (@jschwe, #47029). Similarly, reading system fonts is no longer in the critical path of starting up the engine (@Narfinger, @jdm, #46476).

There were were also a number of savings in the final binary size (@jschwe, @kkoyung, @Narfinger, @jschwe, #47211, #47214, #47210, #46950).

We fixed crashes related to media playback (@calvaris, #46891), the 2d canvas renderer (@yezhizhen, #46915), fonts with negative line gaps (@jschwe, #47374), and resolving fonts variants (@simonwuelker, #47356).

Canvas renderer worker threads can now be adjusted by the thread_pool_canvas_workers preference, allowing more performance granularity according to embedder needs. (@jschwe, #46691, #47018)

We’ve continued our long-running effort to use the Rust type system to make Servo’s integration with SpiderMonkey safer and more reliable (@jdm, @treetmitterglad, @Narfinger, @Gae24, #47398, #47296, #47051, #47005, #47323, #47297, #47322, #47368, #47446, #47317). We’re also working on statically preventing a footgun that can lead to uncollectible GC cycles and leaking memory (@Gae24, #47355, #47650).

Historically, about:memory has reported all memory usage by Rust implementations of JS APIs as one undifferentiated js/malloc-heap number. We now break it down by memory usage of nodes in document trees (@pylbrecht, #46931) and interfaces that are not part of the DOM (@jdm, #47531). We also report memory usage for the network stack’s cookie database (@Narfinger, #47248) and the canvas renderer backend (@janeoa, @jdm, #46958).

We’ve added an experimental threadboost mechanism (@jschwe, @mrobinson, #46843, #47027) that has been observed to improve Speedometer results by 50% and allow canvas rendering to reach 60 FPS. This is initially enabled for OpenHarmony, but future expansion to other Linux-based platforms is expected.

More on the web platform

We upgraded to resvg 0.48, fixing many issues with SVG images with missing width/height attributes that specified a viewBox (@nicoburns, #46937).

Upgrading to Taffy 0.14 fixed a number of CSS grid-related crashes, support for grid names, better intrinsic sizing, and improved performance (@nicoburns, #47031, #47493). We also fixed some issues in the Taffy grid integration for more accurate baselines (@nicoburns, #47518).

Session history traversals (i.e. navigating backwards or forwards in history) now wait for any outstanding traversal to complete (@mrobinson, #47293, #47485). Meanwhile, navigations to about:blank are skipped if the initial about:blank document is present (@jdm, #47074).

about:blank documents no longer use the asynchronous HTML parser (@jdm, #47050), and no longer report a readyState of LOADING (@mrobinson, #47450). Opening auxiliary windows will wait to dispatch the load event until the initial about:blank document has been replaced (@jdm, @mrobinson, #47442, #46975).

For non-about:blank content, we also made the document loading phases more reliable (@TimvdLippe, @mrobinson, #47426), improved conformance of javascript: URL evaluation and navigation target selection (@mrobinson, #47486, #47516), and addressed longstanding compatibility issues with cross-origin Window and Location objects (@mrobinson, #47549).

Our media playback has improved; we fixed several issues around canPlayType() on HTMLMediaElement that allow Servo to report that MP4 content is playable (@jdm, #47612, #47641, #47670).

Input elements with the autofocus property inside of a <dialog> now receive focus when that dialog is opened (@skyz1, @mrobinson, #45826).

We improved the exception error text for numerous web APIs (@jdm, @eachra-bawn, #46960, #47124, #47168, #47580, #47430, #47127).

We also fixed issues related to many other APIs, including:

• matching other browsers’ treatment of Access-Control-Allow-Headers (@yezhizhen, #47600)
• WebCrypto CryptoKey usage checks (@kkoyung, #47112, #47141, #47178) and key lengths (@kkoyung, #47452, #47453)
• determining referrers when navigating (@mrobinson, #47487)
• reading name on Window inside of iframes (@TimvdLippe, @jdm, #47270)
• many edge cases around determining dirty roots for incremental layout (@mrobinson, #46906)
• edge cases around compareDocumentPosition on Node (@SimonSapin, #46886)
• resolving ties in web font matching (@simonwuelker, #47449)
• Range.getClientBoundingRect()/getClientRects() for empty ranges (@yezhizhen, #47143)
• JS module fetching failures can now be retried (@Gae24, #46919)
• KeyEvent.keyCode values for many nonprintable keys now match other browsers (@eachra-bawn, #47461)
• making timing on Performance return a PerformanceTiming object (@jdm, @aniebietafia, #46990)
• synthesizing font variations from font-style (@simonwuelker, @mrobinson, #46918, #47364)
• the Get Element Tag Name WebDriver command (@yezhizhen, #47216)
• removed nonstandard WebDriver-related properties on the global object (@mrobinson, #47542)
• sniffing RAR responses correctly (@wood-ghost, #47366)
• Attribute nodes created during parsing now have the expected namespace prefix (@Ms2ger, #47030)
• improving text-transform: capitalize (@mrobinson, #46910)
• zero-sized margins inside of inline boxes (@Loirooriol, #47020)
• incorrect buttons values in pointer capture transitions (@steigeo, #45628)
• empty lists returned by load() on FontFaceSet (@simonwuelker, #47564)
• cancelling more ongoing network requests when performing a navigation (@mrobinson, #47576)
• shaping text across inline boxes (@mrobinson, #46829)
• scrollable overflow for position: sticky (@rayguo17, #43766)
• fixing hyperlinks for blob: URLs (@TimvdLippe, #47226)
• firing the error callback for decodeAudioData on BaseAudioContext (@amittenak47, @jdm, #46870)

New contributors

A special thanks to the following people for landing their first patch in Servo:

• Frans Skarman (@TheZoq2, #46938)
• Moamen Hesham (@moamenhesham0, #47391)
• Miles Wirht (@philocalyst, #46996)
• Vaibhav Srivastava (@vaibhav8a, #47626)
• wood-ghost (@wood-ghost, #47366)
• 禾可 (@Lfan-ke, #47514)

Interested in helping build a web browser? Take a look at our curated list of issues that are good for new contributors!

Donations

Thanks again for your generous support! We are now receiving 8128 USD/month (+3% from July) in recurring donations. This helps us cover the cost of our speedy CI and benchmarking servers, one of our latest Outreachy interns, and funding maintainer work that helps more people contribute to Servo.

Servo is also on thanks.dev, and already 36 GitHub users (+1 from July) 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.

We now have sponsorship tiers that allow you or your organisation to donate to the Servo project with public acknowlegement of your support. If you’re interested in this kind of sponsorship, please contact us at join@servo.org.

Use of donations is decided transparently via the Technical Steering Committee’s public funding request process, and active proposals are tracked in servo/project#187. For more details, head to our Sponsorship page.