bug#57669: 29.0.50; C-n, C-p off under long lines

[dick]

There might be.  I don't have enough user (that's right: I wasn't
presumptuous enough to use the plural) to know.  My immediate response
however is your own,

"I bet that we won't have a single bug report about this."

First you would need to construct a pathological case, like lots of Urdu
and Hindi, then you would need the geometries to be sufficiently extreme
that a user would notice that the page didn't quite scroll up or down
the full page.  Then you'd need me to renege on "perfect is the enemy of
the good."

I would add that unless you're seriously considering replacing narrowing
with my first-principles scheme (doubtful given how many hours you've
invested in narrowing), this is all an academic exercise in
oneupsmanship, which mind you, I am definitely game for.  If that
suggests I believe I dealt with long lines better than you, you'd be
correct.