The extension won't support multiple user simultaneously. It would require a complete rewrite and would add a staggering amount of complexity. Just use different firefox profiles for each user, which this Multi-Account-Container seem to be basically, just less separated.

It clearly says: "DISCLAIMER: No pricing provider is 100% accurate all the time. Take these prices as advisory, always with a pinch of salt. You should not rely on them solely when doing your trades."