The new previous / next buttons introduced in #831 don't have a focus style in Firefox. They rely on the browsers native outline, and in Firefox the outline doesn't work when unsetting the borders.
To reproduce:
use Firefox (mac or Windows)
tab to the previous and next buttons:
there's no focus style, this prevents users from understanding where focus is
The new previous / next buttons introduced in #831 don't have a focus style in Firefox. They rely on the browsers native outline, and in Firefox the outline doesn't work when unsetting the borders.
To reproduce: