Mozilla has released Firefox 151, the latest update to its popular open-source web browser, with the ability to merge multiple PDFs directly in Firefox’s PDF viewer. With this change, users can now combine PDF files without relying on a separate desktop app or online service.
Firefox 151 also brings local profile backups to Linux and macOS, which lets users create local backups of their Firefox profile and restore them across platforms. Moreover, Mozilla has improved extension and theme restoration, so those installed in a Firefox Desktop profile directory can be restored after moving the profile directory to another location or operating system.
On the privacy side, Standard Enhanced Tracking Protection now includes stronger fingerprinting protections, reducing system information exposed to websites. Firefox 151 also expands local network access restrictions to all users, requiring websites to request permission before connecting to devices on the user’s local network or to apps and services running on the same device.
On top of that, Private Browsing Mode gains a new option to clear all data from the current private session without closing the browser.
On macOS, Firefox 151 improves platform integration with OS-native menus for HTML select dropdowns. URLs copied from iOS devices through Apple’s Universal Clipboard now paste correctly in Firefox.
Copied and pasted images also receive improvements, with Mozilla fixing an issue where maximized Firefox windows could reopen on the wrong monitor after relaunching in multi-display setups.
Firefox 151 also includes a few UI and platform changes. The search bar in Firefox Settings is now larger and spans the full Settings column. On Windows, geolocation respects the operating system’s location permission setting instead of overriding it after a page-level permission is granted.
Firefox for Android gains a toolbar gesture to quickly open the tab list by swiping vertically over the toolbar. The Android version also adds a new AI Controls section in Settings for managing AI-enhanced features.
For web developers, Firefox 151 introduces support for the Web Serial API, allowing websites to communicate with supported serial devices such as microcontrollers, development boards, 3D printers, and CNC machines. The release also adds support for the Document Picture-in-Picture API, enabling pages to place content in an always-on-top popup window.
Other web platform changes include support for declarative slot assignment behavior for shadow roots, improvements to absolutely positioned elements across multi-column containers and printing, and updates to implicit anchors in CSS Anchor Positioning. The release also adds support for the Fullscreen Keyboard Lock API, which allows websites to request stricter fullscreen keyboard handling.
Those eager to download this update immediately can do so directly from Mozilla’s servers.
Windows and macOS users will get an over-the-air update in the next few days. Linux users should see Firefox 151 in their distro repositories soon, too.
