Disabled links accessible via keyboard (tab)

[jonnysp]

Disabled links (a) accessible via keyboard (tab) on latest firefox win 10.

in navbar

disable button

[patrickhlauke]

see https://getbootstrap.com/docs/4.0/components/buttons/#link-functionality-caveat

this advice should probably be replicated in the navbar part of the documentation, and in both cases the examples should probably include tabindex="-1"