29 Sep 2026

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Mozilla Addons Blog: Nova is here: what changes for your Firefox theme

On September 29, Firefox 157 shipped Nova, the biggest refresh of the Firefox interface since Proton back in 2021. The browser frame is cleaner, the sidebar plays a bigger role, and vertical tabs are a first-class layout. Your theme continues to load, and most color and image properties work as they did before.

What does change is where those colors and images display, how some of them look next to each other, and a handful of properties that no longer have a visible effect. Most themes will look fine. Some, especially themes built around a background image, look different enough that you will want to take a look.

This post walks through what changed compared with the Proton interface, what to check in your theme, and what is still being worked on. If you only have five minutes, jump to the checklist.

What changed in the browser frame

The toolbar and sidebar now sit flush with the window edges, with no gaps between them.

For your theme, this means your frame color and background image have less empty space around them, and the edges where the toolbar, sidebar, and page meet are more visible.

Area Proton Nova (Firefox 157)
Toolbar and sidebar Flush with the window, no gaps or floating borders Same as before
Horizontal tabs Theme background applied to the tab strip Same as before
Vertical tabs Tab bar color on the tab strip Tab bar color also shows on the toolbar
Sidebar Separate panel Shares the theme background with the toolbar area

colors, accents and tabs

Accent color. The default Firefox theme uses Nova's purple accent. Every other theme, including yours, uses the operating system's accent color for buttons and other accented controls. Themes cannot set the accent color through the manifest, and is why your theme cannot show the purple you see in the default theme.

Focus and link colors. Firefox still applies its own blue and cyan to focus rings and some links when a theme other than the default is active.

The selected tab. Proton always drew a shadow under the selected tab, which helped it stand out even when a theme did not style it. Nova removes that shadow. If your theme relies on it, the selected tab can blend into the tab strip. Set the selected tab colors, with tab_selected and tab_line, so the selected tab stands out.

Button hover colors. Your button_background_hover and button_background_active colors also apply to buttons on the tab strip, and for buttons that sit on your frame background with vertical tabs. A solid color picked to match the toolbar can almost disappear there. Semi-transparent colors, for example rgba(0, 0, 0, 0.15) for hover and rgba(0, 0, 0, 0.3) for pressed, work on both backgrounds.

Sidebar and vertical tabs

Properties that changed or no longer work

Some theme properties behave differently in Nova. Your theme still loads if it uses them; they just have no visible effect, or style something different.

Property In Nova
ntp_text No longer styles the new tab page search box
popup_text No longer styles the address bar dropdown; other popups still use it
sidebar_highlight No visible effect; the default highlight color is used
sidebar_highlight_text No visible effect
toolbar_bottom_separator Acts as a separator next to or below the toolbar and around the page

The theme manifest reference on MDN is being updated with these changes.

Themes with background images

Themes using images are where you are most likely to see a difference. Your image can now show behind the sidebar and vertical tabs, and an image designed for a wide, short toolbar rarely looks good stretched or tiled down a vertical panel. In our testing of popular themes, the image themes that look off in the sidebar mostly did before Nova too. We did test a number of themes but we invite you to do your own testing. Nova makes the sidebar more visible, so the issues are easier to notice.

You can now choose where your images go with the backgrounds_area property, available from Firefox 156:

If your image was made for the toolbar only, "top_toolbars" with a frame color that suits the image is usually the quickest fix.

Also set a toolbar color, even a semi-transparent one. Without it, notification bars that appear above the page sit directly on your image and can be hard to read.

New Gradient Support

Nova's color themes use gradients, and you can too. The Nova theme manifests are the best working example; look at how they set colors for each surface, including the sidebar. backgrounds_area applies to gradients the same way it applies to images. Older versions of Firefox ignore color properties they don't recognize, so your theme still loads there; if you use a feature older versions reject, set strict_min_version in your manifest.

Checklist: what to check in your theme

Install your theme in Firefox 157 and look at it in each of these states:

  1. Horizontal tabs and vertical tabs.
  2. Sidebar closed, open, and expanded on hover. Also toggle "Customize sidebar" while the sidebar is open or expanded.
  3. Compact density, if your users are likely to use it (under settings -> appearance density(.
  4. A private window.
  5. Light and dark system settings, since the accent follows the operating system.
  6. Hover over the buttons on the tab strip.

Then, if something looks off:

What we are still working on

Nova will evolve after launch. Firefox 158 ships on October 13 with the expand-on-hover sidebar fix. We are also working on these, with no release date yet:

We will post again when these land.

For users who prefer the old look

Some of your users may miss Proton. From September 29, Mozilla is featuring a Firefox Proton theme in the Add-ons Manager for anyone who wants the previous look. It is a normal theme, so users can switch between it and yours at any time.

Resources

Questions?

We want your theme to look its best in Nova. If something looks wrong and the checklist does not fix it, tell us on Discourse and include a link to your theme and a screenshot. Those reports help us find the cases that need a Firefox fix rather than a theme change.

Thank you for making Firefox look like you and like your users.

The post Nova is here: what changes for your Firefox theme appeared first on Mozilla Add-ons Community Blog.

29 Sep 2026 3:34pm GMT

The Mozilla Blog: More modern. More flexible. Still Firefox.

What comes to mind when you think of Firefox? Is it our best-in-class privacy features and ad blocking capabilities? Our partnerships with Wrexham, NVIDIA or Mistral? Or maybe our adorable mascot Kit?

If you've been following Firefox this year, you've seen us add new ways to get things done while giving you more choice over how you browse. That includes browsing two pages side by side, adding an extra layer of privacy with built-in VPN, blocking trackers for smoother scrolling and faster load times, and deciding how AI shows up in Firefox.

For the past few months, many of you have also been trying out our new Firefox design in Nightly and sharing your thoughts with us as we continued to refine the experience.

Today, we're rolling out that design with FX 157 to everyone using Firefox across desktop and mobile devices. Firefox has done a lot of growing over the last year; now it looks the part.

A more modern Firefox

When we first shared our plans to design Firefox for the future, we said we wanted Firefox to feel "current, but not generic. Warm, but still precise."

That design ethos now carries across all of Firefox. We've refreshed the colors, icons and themes throughout the browser, from the tabs and toolbars you use every day to your New Tab page, Private Browsing experience and more, with no cost to your browser performance.

This shared design language across desktop and mobile gives Firefox a consistent foundation for new features and experiences, while keeping the personality that makes Firefox unique.

Make Firefox yours

We've added more choices for how Firefox looks and works, including the return of a feature many of you asked for:

Compact Mode is back. As people started trying the new design, we heard from many of you who wanted to fit more into your browser window. Compact Mode reduces the size of your tabs and toolbar to give more of your screen to the web, with an auto-compact option for smaller screens.

Find your look. A new theme picker makes it easier to explore different looks for Firefox, with new themes and wallpapers to choose from.

Set up New Tab your way. Choose what you want to see on your homepage. Now, you have a dedicated space to pin and organize shortcuts so sites you use all the time stay put.

Refined, not reinvented

Themes and wallpapers may change over time, but the things that made people choose Firefox in the first place are still the same. We're still independent and open source, with privacy protections built into the browser and controls that put you in charge of how Firefox works for you.

This carries through everything we build, from the height of your toolbars and what belongs on your New Tab page to which AI features show up in your browser, which model you choose and what context you want it to have.

Today's Firefox is a renewal, grounded in the same principles that have shaped it from the beginning, with a new design built to carry Firefox forward.

For those who have come with us on this journey, thank you for helping us shape the future of Firefox.

If you've been away on hiatus, welcome back. Try the latest Firefox and let us know what you think.

The post More modern. More flexible. Still Firefox. appeared first on The Mozilla Blog.

29 Sep 2026 1:00pm GMT

28 Sep 2026

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Firefox Nightly: Shoutout to More Layouts – These Weeks in Firefox: Issue 210

Highlights

Friends of the Firefox team

Resolved bugs (excluding employees)

Script to find new contributors from bug list

Volunteers that fixed more than one bug

New contributors (🌟 = first patch)

Project Updates

Add-ons / Web Extensions

Addon Manager & about:addons
WebExtension APIs

DevTools

External contributions
Team/Project Update

WebDriver

Fluent

Lint, Docs and Workflow

Information Management/Sidebar

New Tab Page

Picture-in-Picture

Search and Urlbar

Address Bar
Search
Places

Tests

28 Sep 2026 7:31pm GMT