Recent update to FF 35 is causing behat fails.
It's a know issue with selenium https://vaadin.com/forum#%21/thread/9041799/9061042
David Monllao: Spotted this and provided workaround for it.
downgrade to firefox 34
I (ubuntu synaptic) had to select firefox -> package -> force version -> 34 and also firefox -> package -> lock version so it will not be autoupgraded tomorrow again