Mouse pointer doesn't change to finger icon over hamburger menu.

[calumcraig]

Steps to reproduce:

1. Launch https://hub.safedev.org/
2. Resize browser window so top nav bar collapses to a hamburger menu:
   
3. Hover mouse over hamburger icon.

Expected:
Mouse pointer changes to finger icon (as it does hovering over links).
Actual:
Mouse pointed does not change:

[calumcraig]

Found on Firefox, reproduced on Chrome.