Firefox 144 for developers
This article provides information about the changes in Firefox 144 that affect developers. Firefox 144 is the current Nightly version of Firefox and ships on October 14, 2025.
Note: The release notes for this Firefox version are still a work in progress.
Changes for web developers
Changes for add-on developers
- Adds the ability to specify the style origin for CSS injections from
"content_scripts"manifest key, inscripting.registerContentScripts()with thecssOriginproperty onscripting.RegisteredContentScript, and thecssOriginproperty incontentScripts.register. The style origin can be"user", to add the CSS as a user stylesheet, or"author", to add it as an author stylesheet. Default, to the"author"origin. These properties are case-insensitive. In addition, the value of theoriginproperty ofscripting.insertCSS()is now case insensitive. (Firefox bug 1679997)
Experimental web features
These features are shipping in Firefox 144 but are disabled by default.
To experiment with them, search for the appropriate preference on the about:config page and set it to true.
You can find more such features on the Experimental features page.