Firefox Extension Manifest V3 Migration: What Actually Changed Manifest V3 (MV3) has been a contentious topic in browser extension development — mostly because of Chrome's aggressive changes to blocking WebRequest API. Firefox's approach is different and more developer-friendly. Here's what actually changed and what you need to know. The Short Version for Firefox Firefox's MV3 implementation is more permissive than Chrome's: Blocking WebRequest still works (unlike Chrome, which deprecated it) Background pages → service workers (same as Chrome) Browser action → new unified action key browser_action / page_action → deprecated, use action What Actually Changed in manifest.json Version declaration // MV 2 { "manifest_version" : 2 } // MV 3 { "manifest_version" : 3 } Enter fullscreen mode Exit fullscreen mode Action key // MV 2 { "browser_action" : { "default_popup" : "popup.html" , "default_icon" : "icon.png" } } // MV 3 { "action" : { "default_popup" : "popup.html" , "default_icon" : "icon.png" } } Enter…