Firefox 156 Speeds Up PDF Loading by 45% and Adds macOS Autostart

Mozilla has released Firefox 156.0, which includes faster PDF loading, reduced resource consumption when displaying large JPEG images, a new macOS startup option, and a number of fixes. Firefox 156.0 was made available to users on the Release channel on September 15, 2026.

Firefox 156 Performance, macOS Startup, and Address Bar Changes

The built-in PDF viewer in Firefox is now up to 45% faster to start up. Mozilla has also improved both memory and CPU usage when Firefox is displaying large JPEG images that have been scaled down to fit a page.

Windows PCs that use ARM64 processors have received a performance adjustment for video calls, with WebRTC calls on these devices now having the option of using hardware-based H264 decoding rather than falling back to software decoding.

On macOS, Firefox will now start up automatically when the computer is turned on. Users can enable this option in the Startup section of Firefox Settings.

In France, Germany, and Italy, Firefox 156 extends address bar suggestions to include localized Wikipedia results and occasional sponsored suggestions. Users can turn these off via the Firefox Suggest settings.

Firefox 156 Media, Bookmark, and Network Fixes

A number of fixes address issues with images, audio, and video. Mozilla has corrected a bug that could cause an image to be replaced by a long string of text when a user dragged it to a different position within a rich-text editor.

High-sample-rate FLAC audio stored in MP4 files now plays properly on sites like Bilibili. Mozilla has also fixed an issue where subtitles did not appear in a Picture-in-Picture window when they were enabled after the window had already been opened.

A fix was applied to bookmark handling in cases where a folder and its bookmarks are selected together and then dragged in the Bookmarks sidebar, which could previously cause bookmarks to be moved out of their folder.

In Split View, reversing the two panes could cause the find bar to become permanently unavailable in the affected tab. Mozilla has resolved this problem.

The update also addresses cases where websites failed to load when DNS over HTTPS was enabled and the site itself did not support HTTPS. Mozilla corrected a network issue affecting users of Firefox’s built-in VPN, where Firefox could lose all network connectivity while the VPN was in use. Windows users also received a fix for a problem where Firefox could prevent an auto-hiding taskbar from appearing.

Firefox 156 Security Patches and Enterprise Policy Changes

The security patches included in Firefox 156 carry a high overall impact rating. They are described in Mozilla Foundation Security Advisory 2026-90, published on September 15, and cover vulnerabilities relating to privilege escalation, use-after-free flaws, incorrect boundary conditions, site isolation, sandbox escapes, mitigation bypasses, and other issues.

Notable vulnerabilities include CVE-2026-92005, a use-after-free flaw in the Audio/Video Web Codecs component, and several privilege-escalation vulnerabilities related to Graphics: CanvasWebGL. The advisory also covers high-impact issues in WebExtensions, Graphics, Disability Access APIs, DOM Service Workers, DOM Core and HTML, the Remote Settings Client, WebRender, the HTML parser, XML, SVG, and networking components.

Enterprise administrators received policy changes and fixes with the Firefox 156 enterprise release notes, most of which also apply to Firefox ESR 153.3.0 unless Mozilla states otherwise.

The FirefoxHome policy now includes a Widgets setting that allows new-tab widgets to be enabled or disabled via an Enabled option, with individual widgets blockable through a Blocked setting. Firefox 156 also adds a DisableServiceWorkers option within SitePolicies, allowing service worker registration or use to be blocked on specific sites.

The DisableLaunchOnLogin policy is now applicable on macOS following the addition of the launch-on-login feature, though Mozilla notes this change does not extend to Firefox ESR.

Enterprise fixes address several existing policy issues: startup and in-product actions for setting the default browser now comply with DefaultBrowserSettingEnabled settings; Page Info now consistently disables cookie permission controls set via policy; the New Private Window item no longer appears in the File menu when DisablePrivateBrowsing is active; the Discover extensions button is hidden when extension installation is blocked by InstallAddonsPermission; and new-tab customization controls are disabled when the corresponding FirefoxHome preferences are locked.

Firefox 156 Developer Changes and Availability

Web developers will find that the CSS text-box-trim property now uses the font metrics of a ::first-line pseudo-element where applicable. Mozilla states this behavior aligns with other browsers and the specification.

Firefox 156.0 is available now, with Release channel users having received it on September 15, 2026. Given the high-impact security updates included in this release, updating is strongly recommended. Enterprise administrators can consult the individual enterprise release notes for full details on policy changes, most of which also apply to Firefox ESR 153.3.0.