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.
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Joined June 2009
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- Following5.5K
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Firefox for Web Developers retweeted
When and how CSS custom property values are calculated might not be what you expect, and it has a big impact on your styles…
Firefox for Web Developers retweeted
📝 When and how CSS custom properties are calculated might not be what you expect, and it has a big impact on your styles.
Here's how it works: jakearchibald.com/2026/css-c…
Firefox for Web Developers retweeted
I made an accessibility error when coding up some tooltips. Here's where I went wrong, and how you can avoid making the same mistake:
jakearchibald.com/2026/my-to…
Firefox for Web Developers retweeted
CSS contrast-color is newly baseline, but it falls short in some areas. Here's how it works, and what to look out for:
Firefox for Web Developers retweeted
hasUAVisualTransition landed in Firefox 149, making it available across all major engines. As well as having a very catchy name, it lets you avoid doubling up on page transitions. Here's how it works:
Firefox for Web Developers retweeted
View Transition Types are newly baseline! These make it easier to build transitions that are specific to particular situations.
Also, we have some new View Transition DevTools in Firefox 147…
Firefox for Web Developers retweeted
Ever wish HTTP status codes were easier to remember? 🖼️
Check out this MDN cheatsheet that pairs each status code with an emoji to help you visualize what each one means, from 200 OK ✅ to 418 I’m a teapot 🫖
Check it out 👇
ALT A colorful infographic titled “MDN HTTP Code Cheatsheet with Emojis.” It categorizes HTTP status codes using emoji-enhanced lists grouped by status code classes.
Firefox for Web Developers retweeted
Let's learn about CSP (Content Security Policy) 🛡️
CSP, when set properly,
✅ Blocks malicious scripts from running on your site.
✅ Prevents data injection attacks.
✅ Reduces the risk of clickjacking and other web security threats.
Learn more 👇
developer.mozilla.org/en-US/…
Firefox for Web Developers retweeted
Firefox 146 ships improvements for CSS devs 🎨
• contrast-color() for WCAG-friendly contrast
• display-p3-linear color space
• text-decoration-inset
• scope at-rule now on by default
• -webkit-fill-available for better compat
Release notes 👇
developer.mozilla.org/en-US/…
Firefox for Web Developers retweeted
Mastering layout = Mastering Flexbox
Test your understanding with MDN’s hands-on Flexbox exercises. No setup needed, just code and see what happens, with interactive scrims ✨
💡 Learn by solving
developer.mozilla.org/en-US/…
Firefox for Web Developers retweeted
Fine-tune multilingual typography with text-autospace ✨
It lets you control spacing between CJK and Latin characters.
> text-autospace: ideograph-alpha ideograph-numeric punctuation;
Now available on Baseline 2025. 🎉
Learn more 👇
developer.mozilla.org/en-US/…
Firefox for Web Developers retweeted
Last week I posted about a secret config in Firefox that made view transitions easier to debug.
@SailorPsy said we should make it less secret.
So we did.
Firefox for Web Developers retweeted
Ever wish HTTP status codes were easier to remember? 🖼️
Check out this MDN cheatsheet that pairs each status code with an emoji to help you visualize what each one means, from 200 OK ✅ to 418 I’m a teapot 🫖
Check it out 👇
ALT A colorful infographic titled “MDN HTTP Code Cheatsheet with Emojis.” It categorizes HTTP status codes using emoji-enhanced lists grouped by status code classes.
Firefox for Web Developers retweeted
Happy #DebianDay!
Happy 32nd birthday to @debian, one of the oldest operating systems based on the #LinuxKernel, and the basis for #Ubuntu, #Kali, and #LinuxMint! 🐧🎈🎂
Thank you, #Debian community, for all your amazing work!
@ubuntu @linuxmint @kalilinux
Firefox for Web Developers retweeted
Do you test? You should. 🧪
MDN's testing curriculum covers key testing techniques like unit testing, integration testing, and functional testing, giving you the skills to build and maintain error-free applications.
Start with fundamentals 👇
developer.mozilla.org/en-US/…
Firefox for Web Developers retweeted
📈 We’ve done over 47 million scans and insights into 6.5 million websites.
MDN Observatory is your go-to for the latest security trends and guidelines. Stay ahead of threats with the analysis!
Check your site now 👇
developer.mozilla.org/en-US/…
Firefox for Web Developers retweeted
[Nightly Blog] Turn Tabs To Their Side – These Weeks in Firefox: Issue 177 blog.nightly.mozilla.org/202…
Firefox for Web Developers retweeted
Are you still not using JavaScript Sets?
Discover ↓
✨ set.union()
✨ set.intersection()
✨ set.difference()
See how sets might make your data efficient. Dive in! 👇
developer.mozilla.org/en-US/…
Firefox for Web Developers retweeted
ICYMI ⚠️
JavaScipt date object has been tricky for years, and it's changing soon.
The NEW Temporal API brings,
🌍 Easily handle time zones
📆 Precise date math
🕒 Parse ISO strings without errors
⌛ Durations, date ranges, and more.
Start exploring 👇
developer.mozilla.org/en-US/…