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title Firefox 151 release notes for developers (Beta)
short-title Firefox 151 (Beta)
slug Mozilla/Firefox/Releases/151
page-type firefox-release-notes-active
sidebar firefox

This article provides information about the changes in Firefox 151 that affect developers. Firefox 151 is the current Beta version of Firefox and ships on May 19, 2026.

Note

The release notes for this Firefox version are still a work in progress.

Changes for web developers

Changes for add-on developers

  • The {{WebExtAPIRef("webRequest.onErrorOccurred")}} event now falls back to NS_ERROR_NET_ON_RECEIVING_FROM instead of a string starting with NS_ERROR_NET_ON_ or NS_ERROR_NET_UNKNOWN_. This change is part of performance and reliability improvements to the onErrorOccurred event. ([Firefox bug 1(https://bugzil.la/1881986))
  • {{WebExtAPIRef("tabs.group()")}} and {{WebExtAPIRef("tabs.ungroup()")}} now correctly add and remove a split view when a call includes one of the split view's tabs. Previously, a call would fail or separate the split view. (Firefox bug 2029099)
  • {{WebExtAPIRef("tabs.move()")}} now correctly moves a split view to the right when a call includes one of the split view's tabs. Previously, a call moved a split view only to the left or to the end of the tab list. (Firefox bug 2027855)

Experimental web features

These features are shipping in Firefox 151 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.