Firefox 157 arrives with its biggest redesign in years

Firefox 157 started rolling out this September 29, and the first thing that catches your eye happens before a single page loads: Firefox looks different.

Mozilla had been working for months on a visual overhaul that internally appeared associated with Project Nova. We're not talking about changing a couple of icons and moving a button. Tabs, menus, panels, colors, spacing, and a good chunk of the controls are getting Firefox's biggest visual adjustment in years.

There's also a small quirk typical of a release that's happening practically as I write this: some official Mozilla pages still identified Firefox 157 as Beta or as scheduled for release on September 29, while distribution and release coverage had already begun. In other words, the documentation is still catching up.

The Firefox we knew changed quite a bit

Mozilla softened the shapes of the interface. Tabs now have a more rounded look, the different panels follow a more consistent visual language, and the icons were redrawn.

There are also new themes with light and dark variants. Mozilla's intention is for the browser to be more customizable without immediately relying on extensions or external modifications.

Personally, the change that will probably end up being the most useful is far from being the most spectacular.

Compact Mode returns

Compact Mode is back.

Mozilla had already downplayed this option previously, but users kept asking for it. Firefox 157 once again offers an interface that reduces the space taken up by tabs and browser bars.

On a large screen it might seem like a minor difference. On a laptop, working with two windows side by side and several tabs open, those pixels start to matter.

Mozilla explicitly acknowledges that it decided to bring back this mode after listening to user requests.

AV1 starts making better use of your hardware

This change will be invisible to many people, but technically I think it's one of the good ones.

Firefox 157 allows video calls via WebRTC to use AV1 hardware decoding on compatible devices.

Until now Firefox could end up processing AV1 in software in situations where the hardware had the capability to do it directly.

The difference is like handing a specialized job to the employee who has exactly the right tool, instead of asking someone else to figure it out manually.

Depending on the device and the application used, that can reduce CPU load during AV1 video.

There are also interesting new features for web development

Firefox 157 includes changes that are less visible to the average user, but important for those of us who build applications.

CSS can better check what the browser supports

Mozilla added support for at-rule() inside CSS compatibility checks.

The practical idea is simple: a web application can more accurately determine whether the browser understands a given CSS rule before relying on it.

For applications that need to work correctly across multiple engines, this helps build compatibility without assuming that Chrome, Safari, and Firefox implement exactly the same things.

WebGPU better manages certain graphics resources

WebGPU is advancing too.

Firefox 157 adds support for TRANSIENT_ATTACHMENT, designed for graphics resources that are only needed during a temporary stage of rendering.

That data can stay in fast memory during the operation and avoid unnecessary traffic to VRAM or even certain graphics memory allocations.

It sounds extremely technical because it is.

But WebGPU is enabling web applications to handle graphics and compute tasks that just a few years ago we would have reserved for native applications. Any improvement in memory management matters.

Mozilla keeps adding AI, but also controls

Firefox's direction in artificial intelligence deserves attention.

Mozilla has been experimenting with smart features inside the browser for a while, and Firefox 157 adds an option in enterprise policies related to SpeechRecognition, which allows enabling or blocking on-device voice recognition.

Additionally, administrators can lock that setting so the user cannot change it.

This may seem irrelevant on a personal computer, but it changes quite a bit at universities, companies, financial institutions, or centrally managed fleets.

Mozilla has an interesting opportunity here: adding AI features while maintaining a clear level of control over which ones can be used.

Changes for businesses

Firefox 157 also fixes several management details.

The policies dashboard can now indicate when a policy was only partially applied and identify which element failed.

Issues were also fixed related to multiple home pages configured through policies and to invalid content type handlers that could cause subsequent settings to be discarded.

These are boring changes until you manage hundreds of computers. Then they stop being boring pretty quickly.

Firefox ESR 140 reaches the end

There's another important detail for IT departments.

With this cycle, Firefox ESR 140 reaches the end of its support period, with 140.17.0 being its final version. The current ESR branch moves on through Firefox ESR 153.

Organizations still using ESR 140 should have this on their radar.

Mozilla also changed how fast it ships Firefox

Firefox 157 arrives as part of a new strategy.

Since September, Mozilla has been working on a release cycle of roughly two weeks, instead of the previous four-week pace.

Mozilla explains that this doesn't mean doubling the number of features. The idea is that finished features and fixes can arrive sooner, reducing the reliance on multiple minor updates between versions.

Firefox 155 shipped on September 1, Firefox 156 on the 15th, and Firefox 157 lands on the 29th.

It's a significant change for a browser that spent years working on longer cycles.

My takeaways

The redesign will get most of the screenshots, but Firefox 157 has more interesting changes underneath.

• Compact Mode returns after user requests.
• WebRTC can take advantage of compatible hardware for AV1.
• WebGPU continues bringing advanced graphics capabilities closer to the web.
• CSS improves its compatibility detection mechanisms.
• Businesses get new controls over features like speech recognition.
• Firefox definitively settles into the new biweekly update cycle.

And all of this still runs on Gecko.

That last point seems especially important to me.

Conclusion

Chrome, Edge, Brave, Opera, and several other browsers share Chromium as their base. Safari uses WebKit. Firefox keeps developing Gecko.

Firefox improving matters even for those who don't use it daily, because it keeps another relevant engine participating in the practical definition of how the web works.

Firefox 157 modernizes its look quite a bit, brings back an option its own users had been asking for, and continues improving its graphics and development platform.

I'll be watching for something more than rounded tabs: how Mozilla's AI integration evolves and how much control the user really retains over it.

Main sources: Mozilla: Inside the new Firefox design · MDN: Firefox 157 for developers