It's explained here https://blog.mozilla.org/addons/2022/05/18/manifest-v3-in-firefox-recap-next-steps/ https://blog.mozilla.org/addons/2022/05/18/manifest-v3-

It's explained here https://blog.mozilla.org/addons/2022/05/18/manifest-v3-in-firefox-recap-next-steps/ https://blog.mozilla.org/addons/2022/05/18/manifest-v3-in-fi... And here https://blog.mozilla.org/addons/2022/10/31/begin-your-mv3-migration-by-implementing-new-features-today/ https://blog.mozilla.org/addons/2022/10/31/begin-your-mv3-mi... Firefox kept support for Event Pages which get direct access to DOM and WebAPIs in the background as well as Web Requests, both of which are not available via Chrome's use of service workers/restricted request API > “One of the most controversial changes of Chrome’s MV3 approach is the removal of blocking WebRequest, which provides a level of power and flexibility that is critical to enabling advanced privacy and content blocking features. Unfortunately, that power has also been used to harm users in a variety of ways Chrome’s solution in MV3 was to define a more narrowly scoped API (declarativeNetRequest) as a replacement. However, this will limit the capabilities of certain types of privacy extensions without adequate replacement. > Mozilla will maintain support for blocking WebRequest in MV3. To maximize compatibility with other browsers, we will also ship support for declarativeNetRequest. We will continue to work with content blockers and other key consumers of this API to identify current and future alternatives where appropriate. Content blocking is one of the most important use cases for extensions, and we are committed to ensuring that Firefox users have access to the best privacy tools available.” I hope FF gets service workers going soon, I haven't followed development closely so I'm not sure what's holding them back besides not wanting to replace Event Pages entirely with it [1]. I tried to build a (non-complicated) extension recently and the service worker API seemed cleaner and modern. 1 https://github.com/w3c/webextensions/issues/72 https://github.com/w3c/webextensions/issues/72