Please read these quotes from these links to better understand why it’s not wrong.
“Extension is a plug-and-play, zero-config, cross-browser extension development tool for browser extensions with built-in support for TypeScript, WebAssembly, React, and modern JavaScript.”
“WebExtensions are a way to write browser extensions: that is, programs installed inside a web browser that modify the behavior of the browser or web pages loaded by the browser. WebExtensions are built on a set of cross-browser APIs, so WebExtensions written for Google Chrome, Opera, or Edge will, in most cases, run in Firefox too.”