Firefox 151 release notes for developers (Beta)
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
webRequest.onErrorOccurredevent now falls back toNS_ERROR_NET_ON_RECEIVING_FROMinstead of a string starting withNS_ERROR_NET_ON_orNS_ERROR_NET_UNKNOWN_. This change is part of performance and reliability improvements to theonErrorOccurredevent. ([Firefox bug 1(https://bugzil.la/1881986)) tabs.group()andtabs.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)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.