Firefox Developer Edition 149.0 download

Version 149.0beta, first offered to Beta channel users on February 25, 2026
Firefox Beta gets updated 3 times a week and as a consequence, the release notes for the Beta channel are updated continuously to reflect features that have reached sufficient maturity to benefit from community feedback and bug reports.
Warning: Features listed here may or may not make a final release of Firefox.
In addition to these release notes, you can follow ongoing development via the Firefox Trains website or our @FirefoxBeta Bluesky account.

New
- The WebRender layer compositor is now enabled on Windows, reducing power usage during full-screen video playback and improving WebGL/WebGPU performance.
- Many PDF files will now load significantly faster thanks to hardware acceleration.
- Address Autofill is enabled for users in Australia, India, Italy, Poland, and Austria
- Firefox now automatically blocks notifications and permanently revokes permissions for any website flagged as malicious by SafeBrowsing. This prevents unsafe sites from sending background notifications to users, commonly used for ads, spam or phishing.
- You can now add a Share button to your toolbar from Customize Toolbar. It lets you easily share the addresss of your current tab using your Windows or macOS Operating system’s sharing services.
- View two pages side-by-side in a single window with the new Split View feature that makes it easier to compare information, research topics, or work across two pages at once. To create a split view, select one or two tabs and choose Add to Split View or Open in Split View.

Fixed
- Increased robustness of HTTP/3 upload performance for unstable network conditions.

Changed
- TrustPanel combines the privacy and security panels accessed from the urlbar to give the user one place to check the privacy & security settings of the current page
- Firefox 149 tightens the security requirements for the JavaScript files that can be loaded in the parent process, to provide defense in depth against security threats.
- On Linux, Firefox will now default to the XDG portal file picker if available, rather than the GTK3 one, which is usually better integrated with the user's desktop environment, and more powerful.
- Firefox error pages have a fresh new look, with updated visuals that better match the overall feel of Firefox. The redesigned pages create a more cohesive experience while making it clearer what went wrong.

Developer
- The toolbar of the Storage Inspector now has a button to delete all entries of the currently selected storage.
- Besides each CSS declaration related to a computed value shown in the Computed view there's now an icon to jump to it in the Rules view.

Web Platform
- showPicker() now supports text-based <input> elements with an associated <datalist>, displaying the autofill dropdown. See documentation.
- The functions xywh() and rect() were previously already implemented for the clip-path and offset-path properties. Now they are also available for the shape-outside property.
- The math value of the CSS font-family is now supported and used by default for MathML's <math> element. It enables Web developers to indicate special fonts with advanced math features should be used. Firefox will rely on the serif font for mathematics defined in Firefox preferences.
- Added support for the HTML attribute popover="hint".
- Enabled media element pseudo-classes, such as :playing, :paused…
- Enabled the spec-compliant HTMLMediaElement.captureStream() API.
- Added support for closing popovers & dialogs with the Android Back Button, and implement the CloseWatcher API for handling this in script.
- The new Reporting API provides a generic reporting mechanism for web applications to use to make reports available based on various platform features (for example Content Security Policy, Permissions-Policy, or feature deprecation reports) in a consistent manner.