I just recently upgraded my forum to version 0.9.0 and have the same issue.
Firefox shows no Settings menu, additionally the user name is not only halfway under the profile picture, but also rendered in white so that it is not shown.
When selecting a custom skin the hamburger button appears in the area marked with the top left red circle.
This could at least help as a workaround for users experiencing the problem.
Edit: I realised from the github discussion that this should be fixed in the current persona master.
I'll wait for 0.9.1 then.