FF has been doing this for ages, going back to at least FF 2.0.x.
It always happens in the Google News page search fields, but
not in most other text entry fields. Safari doesn't do it either.
Leopard, but it used to be there in Tiger too,
and on a different machine also.
It's only a tiny little thing, like a grain of sand
being pushed around by the cursor. Perfection
demands that even the smallest grain of sand
be eliminated! 🙂
ps
Are you sure that's the news page you're looking
at?