Mobile Burger Menu not showing

But please see screen grab of a site in progress - the menu has not become a burger style/responsive menu.

How do I add that functionality on?

I am starting to think WPMU De just hates me (everything I seem to be doing is taking ages/ doesn't work for me...first time, content jumps about and I am strugging with the most obvious of things...) . I use firefox - but if I use microsoft edge I seem to get tooltips appearing (which is more helpful) when i am using wmpuvdev but tooltips don;t work in firefox...

I can't use chrome for using wmpudev as I am designer and I have fonts installed that in chrome renders fonts pretty unreadable ( aknow chrom bug since 2012)