I am really sorry for this. The reason of useless may be you need give the addon permissions to instagram manually. You can see the example here(https://user-images.githubusercontent.com/22173084/241606818-f6988f38-46fc-4c9c-a37e-35a25e71dbe4.png).
Besides,the code is completely open source and the source code was uploaded here(https://github.com/TheKonka/instagram-download-browser-extension). And I promise there are no malicious code.
It is my falut for less description and guidance. I will try fix this.Thanks you for your advice!