We continue to support DOM-based background scripts in the form of Event pages, and the blocking webRequest feature, as explained in
our previous blog post. Chrome’s version of MV3 requires service worker-based background scripts, which we do not support yet. However, an extension
can specify both and have it work in Chrome 121+ and Firefox 121+. Support for Event pages, along with support for blocking webRequest, is a divergence from Chrome that enables use cases that are not covered by Chrome’s MV3 implementation.