Eversyncn Firefox 59.0.2 - Win 10 issue

Hi,

I installed Eversync on Chrome and Firefox on Win7 and on Chrome on Win10 without any problem, but I got an issue on Firefox 59.0.2 Win 10.

At first I installed it but I couldn't log in, I got repeated message "An error has occurred. Return to login."

So I deactivated all other extensions, uninstalled it and tried installing again.

To my surprise it got even worse. 

Eversync icon is broken and there is no menu.

Here is what I get:

Now if I uninstall and reinstall I get the same issue.

Is there a way to delete eversync settings to try a clean install?

Any other help?

Thanks
Alessio