The problem's solved, so my review is corrected too. I should have posted it as an issue at GitHub but I didn't have account there. So my final feedback is:

This extension works great! It simplifies switching between multiple AWS accounts by extending number of accounts beyond 5 and adding color accents under top menu.

----- original review -----
I use it in Chrome and it works great. Is there anything that can be configured to make it working in Firefox 57?