A very handy addon, thanks for sharing.
There is only one UX issue. The github1s appears on the right (instead of the left as in the screenshot) and moves all buttons of place to the left when doing so. Given that the loading takes ~0.5s, it was enough for me to want to click multiple time on the "clone" button just to have it replaced by the "github1s" button.
I don’t think it’s OS/browser dependent, but I’m using mac os catalina with firefox.