The change affects the parts of Firefox people see throughout the day rather than adding a single new tool. Mozilla’s updated interface uses revised colors and icons across tabs, toolbars, Private Browsing and the New Tab page. A new theme picker gives users more appearance options, and Mozilla says users can pin a frequently visited site as a shortcut on the New Tab page. The redesign had been tested in Firefox Nightly for several months before the company began the broader rollout.
Mozilla calls the work Nova internally. Its broader goal is to update the browser’s appearance while retaining familiar controls. The release follows a series of Firefox changes that gave users options around side-by-side browsing, built-in VPN features and AI controls. The September announcement focuses on the interface and customization rather than claiming a change to the browser’s underlying performance.
Compact Mode returns
Compact Mode reduces the height of tabs and the toolbar, leaving more vertical space for a page. Mozilla says it also includes an automatic compact option for smaller screens. The setting addresses a practical trade-off in browser design: larger controls can be easier to see and use, but they leave less room for the document or application open in the window.
People who work on smaller laptop displays or keep several tabs open may prefer the tighter layout. Others may choose the default spacing, especially on touch devices where controls need room. Returning Compact Mode gives users a choice rather than forcing one density across different screens. The feature had been requested by users, Mozilla said, after testers tried the redesigned browser.
Firefox’s updated theme picker also changes how customization is presented. Users can choose among new themes and wallpapers, and pin a shortcut on the New Tab page so it stays in place. Mozilla has also promoted a Firefox Proton theme in the Add-ons Manager for people who prefer the earlier look. Since it is a normal theme, users can switch between it and other themes.
What Nova means for browser themes
The redesign has practical consequences for people who make Firefox themes. Mozilla’s Add-ons Community Blog explains that Firefox 157 changes how parts of a theme appear around the browser frame and sidebar. The toolbar and sidebar now meet the window edges without the previous gaps, and vertical tabs affect where theme colors are visible. Theme authors may need to check their designs in both horizontal and vertical tab layouts, with the sidebar open and closed, and in Compact Mode.
Mozilla says existing themes continue to load, and most color and image properties still work. Some details look different because the browser’s layout has changed. For example, the selected tab no longer has the shadow used in the previous design, so a theme that relied on that shadow may make the active tab harder to distinguish. The Add-ons post gives theme developers specific properties to check and says further theme-related refinements are being worked on, without giving a release date for them.
That developer guidance matters to users who rely on custom themes for contrast or visual distinction. A theme can remain installed yet look different after an interface update. Checking the theme in the new tab arrangements can reveal problems that are not obvious in a default horizontal-tab setup. Mozilla says a Proton theme is available for users who want an approximation of the previous Firefox appearance.
Security updates ship with the browser
Firefox 157 also includes security fixes. Mozilla’s security advisory for the release, dated September 29, lists vulnerabilities fixed in the desktop browser, including bugs in media playback, graphics, networking, storage and sandbox components. The advisory assigns individual CVE identifiers to flaws and describes issues that include sandbox escapes and denial-of-service conditions. Users should install the update through Firefox’s normal update process rather than treating the redesign as a purely cosmetic release.
Mozilla’s release notes are published separately for desktop and Android, and they may contain platform-specific fixes. Firefox 157 for Android was also offered to release-channel users on September 29. The rollout can take time to reach every device, so the version displayed in the browser’s About page is the useful check for whether an installation has updated.
For most users, the visible choice is between the default interface and a denser toolbar, along with new theme and New Tab options. Theme developers have additional compatibility checks to make because Nova changes the browser frame and sidebar. The security advisory provides another reason to install Firefox 157 even for users who do not plan to change their appearance settings.
Sooraj Raj is a programmer, blogger and professional developer with an interest in technology research and publishing. He writes about technology developments and shares information in a clear, straightforward way.
