Hey @cezaraugusto I found @types/firefox-webext-browser to have inferior types to @types/webextension-polyfill.

As an example: in https://github.com/DefinitelyTyped/DefinitelyTyped/blob/981449c691b9be0fca569c48151fc57606f5ea7a/types/firefox-webext-browser/index.d.ts#L4680
the func parameter has a fixed signature of no parameters, although you can (and should) supply args to a scripting function. Meaning that whenever you use args, func incorrectly will report a type error.
Or ExecutionWorld is hardcoded to ISOLATED.

@types/webextension-polyfill more correctly types the args as unknown:
https://github.com/DefinitelyTyped/DefinitelyTyped/blob/981449c691b9be0fca569c48151fc57606f5ea7a/types/webextension-polyfill/namespaces/scripting.d.ts#L38
And ExecutionWorld correctly is type ExecutionWorld = "ISOLATED" | "MAIN"

Which is not insanely good as there could be generics that match args signature to the func params signature, but hey at least it doesn't report wrong type errors as @types/firefox-webext-browser does.

Now the extension.js cli has a dependency on @types/firefox-webext-browser which ambiently declares itself as a global, which is nice in theory but makes overriding it kinda hard. I was successful with (app/types/browser.d.ts):

/// <reference types="webextension-polyfill" />

declare const browser: typeof import('webextension-polyfill')

So it seemed that your references in extension-env.d.ts were not enough somehow and I had to do declare const browser to override firefox-webext-browser properly. Maybe it has to do with me having the extension in a yarn3 monorepo that hoists to root, but it shouldnt make a difference really as tsconfig is confined to the package-level.

My tsconfig is super simple with no types/typeRoot/include shenanigans:

{
  "compilerOptions": {
    "allowJs": true,
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "isolatedModules": true,
    "jsx": "react-jsx",
    "lib": ["dom", "dom.iterable", "esnext"],
    "moduleResolution": "node",
    "module": "esnext",
    "noEmit": true,
    "resolveJsonModule": true,
    "strict": true,
    "target": "esnext",
    "verbatimModuleSyntax": true,
    "useDefineForClassFields": true,
    "skipLibCheck": true
  },
  "exclude": ["node_modules", "dist"]
}