Event Pages
Chrome's version of MV3 introduced Background Service Worker as a replacement for the
(persistent) Background Page. Mozilla is working on extension Service Workers in Firefox for
compatibility reasons, but also because we like that they're an event-driven environment with
defined lifetimes, already part of the Web Platform with good cross-browser support.
We've found Service Workers can't fully support various use cases we consider important,
especially around DOM-related features and APIs. Additionally, the worker environment is not
as familiar to regular web developers, and our developer community has expressed that
completely rewriting extensions can be tedious for thousands of independent developers of
existing extensions.
In Firefox, we have decided to support Event Pages in MV3, and our developer preview will not
include Service Workers (we're continuing to work on supporting these for a future release).