Firefox Tomorrow
Nightly 155.0a1

Firefox Nightly 155.0a1

Monday, July 20, 2026 6 changes 3 categories
New (2) Developer (1) Web Platform (3)

TL;DR

2 new features, 4 other changes. Highlight: Starting with Firefox 154, We’re testing a simpler tab context menu in Firefox Labs. Turn it on in Settings > Firefox Labs > Streamline t…

New 2 items
  1. 01

    Starting with Firefox 154, We’re testing a simpler tab context menu in Firefox Labs. Turn it on in Settings > Firefox Labs > Streamline tab menu and tell us what you think on Mozilla Connect . Bug 2031718

  2. 02

    Starting with Firefox 154, Firefox Nightly now supports QUIC version 2 ( RFC 9369 ) for HTTP/3 connections. Firefox offers both QUIC v1 and v2 using compatible version negotiation ( RFC 9368 ). The server selects which version is used, so connections upgrade to QUIC v2 when the server chooses it and remain on QUIC v1 otherwise. Bug 2040450

Developer 1 item
  1. 01

    Developer Information

Web Platform 3 items
  1. 01

    Starting with Firefox 154, Firefox Nightly now supports the alpha() CSS function. This is a relative color function that can be used to modify just the alpha component of a given color. Bug 2047437

  2. 02

    Starting with Firefox 153, Firefox Nightly ships an experimental implementation of the link-parameters property by Tyler Thrailkill. Bug 2046153

  3. 03

    Starting with Firefox 153, Firefox Nightly now supports two new keywords closest-corner and farthest-corner for the radial size in the circle() and ellipse() functions. Bug 2045278