Set font of the wb-firstHeading toolbar back to sans-serif

I marked a few spots with FIXME. These lines can be removed
in 4 weeks when all caches got flushed.

Bug: 57436

Change-Id: I0865d144c70a726eb97b42a247d32131463bb6df
(cherry picked from commit b9180d4d56987bb068b42b5efc5720a4e6ad0aff)