Firefox for Web Developers
@webdevs.firefox.com
Official Firefox account for people who build on the web. Learn about the things we're working on to grow and improve the web platform.
AV1 won an Emmy! We're proud to be part of the Alliance for Open Media, where the codec was developed. But the story's not over… AV2 is just around the corner.
https://blog.mozilla.org/en/mozilla/av1-video-codec-wins-emmy/
https://blog.mozilla.org/en/mozilla/av1-video-codec-wins-emmy/
December 5, 2025 at 4:59 PM
AV1 won an Emmy! We're proud to be part of the Alliance for Open Media, where the codec was developed. But the story's not over… AV2 is just around the corner.
https://blog.mozilla.org/en/mozilla/av1-video-codec-wins-emmy/
https://blog.mozilla.org/en/mozilla/av1-video-codec-wins-emmy/
Oh hello! We've had a bit of a rename & rebrand (formally FirefoxDevTools), but the content will be roughly the same as it's been for the past few months.
We're looking forward to posting more on web platform & DevTools features.
We're looking forward to posting more on web platform & DevTools features.
December 5, 2025 at 1:38 PM
Oh hello! We've had a bit of a rename & rebrand (formally FirefoxDevTools), but the content will be roughly the same as it's been for the past few months.
We're looking forward to posting more on web platform & DevTools features.
We're looking forward to posting more on web platform & DevTools features.
Another API proposal from TPAC: CSS routes and navigation queries, meaning less JavaScript is needed for view transitions!
https://drafts.csswg.org/css-navigation-1/
https://github.com/w3c/csswg-drafts/issues/8685#issue-1653949919
https://drafts.csswg.org/css-navigation-1/
https://github.com/w3c/csswg-drafts/issues/8685#issue-1653949919
December 2, 2025 at 4:02 PM
Another API proposal from TPAC: CSS routes and navigation queries, meaning less JavaScript is needed for view transitions!
https://drafts.csswg.org/css-navigation-1/
https://github.com/w3c/csswg-drafts/issues/8685#issue-1653949919
https://drafts.csswg.org/css-navigation-1/
https://github.com/w3c/csswg-drafts/issues/8685#issue-1653949919
We have Custom Elements, but do we also need Custom Attributes?
This was discussed at TPAC. Is it something you'd like on the platform?
https://github.com/WICG/webcomponents/issues/1029
This was discussed at TPAC. Is it something you'd like on the platform?
https://github.com/WICG/webcomponents/issues/1029
December 1, 2025 at 2:29 PM
We have Custom Elements, but do we also need Custom Attributes?
This was discussed at TPAC. Is it something you'd like on the platform?
https://github.com/WICG/webcomponents/issues/1029
This was discussed at TPAC. Is it something you'd like on the platform?
https://github.com/WICG/webcomponents/issues/1029
Reposted by Firefox for Web Developers
We (@firefoxdevtools.bsky.social) are having a work week with the folks from @developer.mozilla.org to talk about better collaboration between our teams.
We already have some ideas that we'll share in the future, but it would I'm curious if you have ideas around that topic?
We already have some ideas that we'll share in the future, but it would I'm curious if you have ideas around that topic?
November 25, 2025 at 10:52 AM
We (@firefoxdevtools.bsky.social) are having a work week with the folks from @developer.mozilla.org to talk about better collaboration between our teams.
We already have some ideas that we'll share in the future, but it would I'm curious if you have ideas around that topic?
We already have some ideas that we'll share in the future, but it would I'm curious if you have ideas around that topic?
Out-of-order HTML patching, another proposal from TPAC, lets HTML be presented non-linearly, and a single file can update multiple parts of the page.
Would this feature be useful to you?
Would this feature be useful to you?
November 19, 2025 at 4:10 PM
Out-of-order HTML patching, another proposal from TPAC, lets HTML be presented non-linearly, and a single file can update multiple parts of the page.
Would this feature be useful to you?
Would this feature be useful to you?
streamHTMLUnsafe() was presented at TPAC last week. Finally, an API that lets you easily use the streaming HTML parser from JavaScript! Here's a quick overview:
November 19, 2025 at 12:00 AM
streamHTMLUnsafe() was presented at TPAC last week. Finally, an API that lets you easily use the streaming HTML parser from JavaScript! Here's a quick overview:
Two-phase view transitions, for faster cross-document transitions, were presented at TPAC last week. Here's a quick 3min overview…
https://www.youtube.com/watch?v=A6rO9RGmJgA
https://www.youtube.com/watch?v=A6rO9RGmJgA
Two-phase view transitions
YouTube video by Jake Archibald
www.youtube.com
November 17, 2025 at 3:50 PM
Two-phase view transitions, for faster cross-document transitions, were presented at TPAC last week. Here's a quick 3min overview…
https://www.youtube.com/watch?v=A6rO9RGmJgA
https://www.youtube.com/watch?v=A6rO9RGmJgA
The W3C Security Web Application Guidelines Community Group wants to understand how developers are using specific web platform security features, and what the barriers are to the adoption.
Take their survey here: https://bit.ly/3JR6JML
Take their survey here: https://bit.ly/3JR6JML
Web security survey
Thanks for taking our survey about the usage of web platform security features.
We're the W3C Security Web Application Guidelines Community Group (SWAG CG), and our mission is to develop guidelines f...
docs.google.com
November 13, 2025 at 4:46 PM
The W3C Security Web Application Guidelines Community Group wants to understand how developers are using specific web platform security features, and what the barriers are to the adoption.
Take their survey here: https://bit.ly/3JR6JML
Take their survey here: https://bit.ly/3JR6JML
🚀 Firefox 145 introduces WebDriver BiDi enhancements like a new `emulation.setUserAgentOverride` command for spoofing user agents, a `browsingContext.downloadEnd` event to track completed downloads, plus various fixes.
#Firefox #WebDriver
#Firefox #WebDriver
November 12, 2025 at 6:49 AM
🚀 Firefox 145 introduces WebDriver BiDi enhancements like a new `emulation.setUserAgentOverride` command for spoofing user agents, a `browsingContext.downloadEnd` event to track completed downloads, plus various fixes.
#Firefox #WebDriver
#Firefox #WebDriver
Reposted by Firefox for Web Developers
The @firefoxdevtools.bsky.social JSON viewer got better in @firefoxnightly.bsky.social : the console offers access to the original json data via `$json`.
This allows to easily manipulate the underlying data to get what you want
This allows to easily manipulate the underlying data to get what you want
![Firefox JSON Viewer opened for the html entites JSON file
We can see the various properties of the JSON file, which are all objects containing a "characters" and a "codepoints" properties.
The Console is opened at the bottom. In it, we can see a console message explaining that some data is available (`$json.data` - the parsed JSON object, $json.text` - the original JSON text and `$json.headers` - HTTP request and response headers)
There's a console evaluation done with the following snippet:
```js
Object.entries($json.data)
.filter(([k, v]) => v.codepoints.length > 1)
.map(([k, v]) => ({characters: v.characters, htmlEntity: k, codepoints: v.codepoints}))
```
and the result shows an array of objects containing "characters", "htmlEntity" and "codepoints" properties.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:l6jizqbrtfnhnrd7vmsqmi3n/bafkreigizqr72frwj6qa53onh2tskqmcmrydexkzeydrkrarwiuoyulcmq@jpeg)
November 7, 2025 at 11:40 AM
The @firefoxdevtools.bsky.social JSON viewer got better in @firefoxnightly.bsky.social : the console offers access to the original json data via `$json`.
This allows to easily manipulate the underlying data to get what you want
This allows to easily manipulate the underlying data to get what you want
Reposted by Firefox for Web Developers
Last week I posted about a secret config in Firefox that made view transitions easier to debug.
Folks said we should make it less secret.
So we did.
Folks said we should make it less secret.
So we did.
October 27, 2025 at 10:29 AM
Last week I posted about a secret config in Firefox that made view transitions easier to debug.
Folks said we should make it less secret.
So we did.
Folks said we should make it less secret.
So we did.
New in Firefox nightly (146.0a1 2025-10-19): large lists of unused CSS custom properties are collapsed by default.
This not only reduces clutter, it also massively speeds up the rendering of the inspector panel in some cases.
This not only reduces clutter, it also massively speeds up the rendering of the inspector panel in some cases.
October 21, 2025 at 12:38 PM
New in Firefox nightly (146.0a1 2025-10-19): large lists of unused CSS custom properties are collapsed by default.
This not only reduces clutter, it also massively speeds up the rendering of the inspector panel in some cases.
This not only reduces clutter, it also massively speeds up the rendering of the inspector panel in some cases.
Reposted by Firefox for Web Developers
We're currently working on devtools for view transitions in Firefox, but in the meantime, here's a little-known option that helps…
October 20, 2025 at 2:28 PM
We're currently working on devtools for view transitions in Firefox, but in the meantime, here's a little-known option that helps…
Reposted by Firefox for Web Developers
Well, isn't this handy! The font inspector in #firefox devtools links to the foundry and shows the license (tsk @ unlicensed trial 🧐)
@firefoxdevtools.bsky.social #fonts
@firefoxdevtools.bsky.social #fonts
October 16, 2025 at 9:22 AM
Well, isn't this handy! The font inspector in #firefox devtools links to the foundry and shows the license (tsk @ unlicensed trial 🧐)
@firefoxdevtools.bsky.social #fonts
@firefoxdevtools.bsky.social #fonts
Reposted by Firefox for Web Developers
Firefox 144 now supports INP! 🦊
We just shipped interactionId, the piece that makes Interaction to Next Paint work. It helps browsers connect events from the same interaction and measure how responsive pages really feel.
More here: blog.mozilla.org/performance/...
We just shipped interactionId, the piece that makes Interaction to Next Paint work. It helps browsers connect events from the same interaction and measure how responsive pages really feel.
More here: blog.mozilla.org/performance/...
Firefox 144 ships interactionId for INP – Mozilla Performance
TL;DR Firefox 144 ships PerformanceEventTiming.interactionId, which lets browsers and tools group events that belong to the same user interaction. This property is used to calculate Interaction to Nex...
blog.mozilla.org
October 15, 2025 at 12:46 PM
Firefox 144 now supports INP! 🦊
We just shipped interactionId, the piece that makes Interaction to Next Paint work. It helps browsers connect events from the same interaction and measure how responsive pages really feel.
More here: blog.mozilla.org/performance/...
We just shipped interactionId, the piece that makes Interaction to Next Paint work. It helps browsers connect events from the same interaction and measure how responsive pages really feel.
More here: blog.mozilla.org/performance/...
🦊 Firefox 144 adds the screen orientation and timezone override commands + the downloadWillBegin event to WebDriver BiDi! fxdx.dev/firefox-webd...
Firefox WebDriver Newsletter 144 – Firefox Developer Experience
fxdx.dev
October 14, 2025 at 1:59 PM
🦊 Firefox 144 adds the screen orientation and timezone override commands + the downloadWillBegin event to WebDriver BiDi! fxdx.dev/firefox-webd...
As an experiment, we (the Firefox team) wanted to try a new way to get feedback on which Interop proposals matter most.
So, here's a web app where you can rank the proposals you care about, giving us data we can use when reviewing which ones to champion.
interop-rank.jakearchibald.com
So, here's a web app where you can rank the proposals you care about, giving us data we can use when reviewing which ones to champion.
interop-rank.jakearchibald.com
Interop Feature Ranking
Rank the web platform features you care most about
interop-rank.jakearchibald.com
October 9, 2025 at 5:00 PM
As an experiment, we (the Firefox team) wanted to try a new way to get feedback on which Interop proposals matter most.
So, here's a web app where you can rank the proposals you care about, giving us data we can use when reviewing which ones to champion.
interop-rank.jakearchibald.com
So, here's a web app where you can rank the proposals you care about, giving us data we can use when reviewing which ones to champion.
interop-rank.jakearchibald.com
🦊 Firefox 143 was just released!
Some WebDriver BiDi highlights: new commands to record and retrieve network responses, backfill events for `browsingContext.contextCreated` and, as usual, some bug fixes 🐛.
More details at fxdx.dev/firefox-webd... !
Some WebDriver BiDi highlights: new commands to record and retrieve network responses, backfill events for `browsingContext.contextCreated` and, as usual, some bug fixes 🐛.
More details at fxdx.dev/firefox-webd... !
Firefox WebDriver Newsletter 143 – Firefox Developer Experience
fxdx.dev
September 17, 2025 at 7:06 AM
🦊 Firefox 143 was just released!
Some WebDriver BiDi highlights: new commands to record and retrieve network responses, backfill events for `browsingContext.contextCreated` and, as usual, some bug fixes 🐛.
More details at fxdx.dev/firefox-webd... !
Some WebDriver BiDi highlights: new commands to record and retrieve network responses, backfill events for `browsingContext.contextCreated` and, as usual, some bug fixes 🐛.
More details at fxdx.dev/firefox-webd... !
Reposted by Firefox for Web Developers
Yay! It's the first Firefox release since I've joined the team, so let's take a look at some of the new developer-facing features in Firefox 142… 🧵
August 22, 2025 at 9:55 AM
Yay! It's the first Firefox release since I've joined the team, so let's take a look at some of the new developer-facing features in Firefox 142… 🧵
Reposted by Firefox for Web Developers
Gecko: Intent to Ship: Command and CommandFor attributes
Gecko: Intent to Ship: Command and CommandFor attributes
Gecko: Intent to Ship: Command and CommandFor attributes
groups.google.com
August 18, 2025 at 12:28 PM
Gecko: Intent to Ship: Command and CommandFor attributes
Reposted by Firefox for Web Developers
View Transitions are enabled by default in Firefox Nightly, so they're on their way to stable. Give it a test with your current transitions, and give me a shout if anything doesn't look right.
August 21, 2025 at 8:16 AM
View Transitions are enabled by default in Firefox Nightly, so they're on their way to stable. Give it a test with your current transitions, and give me a shout if anything doesn't look right.
Firefox 142 brings a few WebDriver BiDi and Classic updates: a new command to set the locale override, some changes around handling the cookies 🍪 and setting the proxy, and more at fxdx.dev/firefox-webd... 🚀
Firefox WebDriver Newsletter 142 – Firefox Developer Experience
fxdx.dev
August 19, 2025 at 3:33 PM
Firefox 142 brings a few WebDriver BiDi and Classic updates: a new command to set the locale override, some changes around handling the cookies 🍪 and setting the proxy, and more at fxdx.dev/firefox-webd... 🚀
🦊 Freshly released Firefox 141 comes with a few WebDriver updates. Setup a proxy for a container with browser.createUserContext, monitor history API usage with browsingContext.historyUpdated. And also a few changes around Cookies.
Read more at fxdx.dev/firefox-webd... 🚀
Read more at fxdx.dev/firefox-webd... 🚀
Firefox WebDriver Newsletter 141 – Firefox Developer Experience
fxdx.dev
July 23, 2025 at 8:17 AM
🦊 Freshly released Firefox 141 comes with a few WebDriver updates. Setup a proxy for a container with browser.createUserContext, monitor history API usage with browsingContext.historyUpdated. And also a few changes around Cookies.
Read more at fxdx.dev/firefox-webd... 🚀
Read more at fxdx.dev/firefox-webd... 🚀
🦊 In Firefox 140, WebDriver BiDi allows to override certificates security settings per container and supports a new "navigationCommitted" event. This release also brings a few fixes for action simulation.
More details at fxdx.dev/firefox-webd... 🚀
More details at fxdx.dev/firefox-webd... 🚀
Firefox WebDriver Newsletter 140 – Firefox Developer Experience
fxdx.dev
June 24, 2025 at 4:14 PM
🦊 In Firefox 140, WebDriver BiDi allows to override certificates security settings per container and supports a new "navigationCommitted" event. This release also brings a few fixes for action simulation.
More details at fxdx.dev/firefox-webd... 🚀
More details at fxdx.dev/firefox-webd... 🚀