When I built Weather & Clock Dashboard , I wanted to understand the current state of Firefox extension APIs versus Chrome's Manifest V3 changes. Here's what I learned. Quick Context: Why MV3 Matters Manifest V3 is Google's overhaul of the Chrome extension platform. It's controversial because some changes limit ad-blockers and general-purpose content filtering. Firefox's position : Mozilla implemented MV3 for compatibility, but with key differences that preserve extension power. What Changed in MV3 1. Background Scripts → Service Workers MV2: "background" : { "scripts" : [ "background.js" ], "persistent" : false } Enter fullscreen mode Exit fullscreen mode MV3: "background" : { "service_worker" : "background.js" } Enter fullscreen mode Exit fullscreen mode Service workers are ephemeral — they don't persist in memory. This means you can't hold state in variables across events.…