Firefox text area editor rendering artifacts

Wed Dec 19 13:47:20 UTC 2012

With an up-to-date F18 including updates-testing, in GNOME Shell with
ATI Radeon graphics,…

… in the Firefox text area editor, e.g. when adding comments at
bugzilla.redhat.com, I see rendering errors from time to time.
Such as empty lines hiding my text, damaged lines, duplicated
lines, but moving up and down fixes that again.

Known thing? GNOME Shell specific?

-- 
Fedora release 18 (Spherical Cow) - Linux 3.6.10-5.fc18.x86_64
loadavg: 0.02 0.02 0.05