Firefox 3 has been rendering some corrupted images for me since its
release. Some images would render as fully or partially black, others
would render with bits of Firefox toolbar and even others would render
with different portions of the web page and other X11 applications.
Xorg log would show spammed "Render bad image" messages. Opera renders
correctly, except it breaks malloc (e.g. mplayer will fail to allocate
memory while Opera is running). I've kept ports up to date, and have
even rebuilt all ports, but nothing fixes these problems. These
problems continue to occur on even the latest 7-STABLE builds.
I myself have had this issue for a little while myself. Pictures
partially display and rest black or picture displays as complete back or
as also mentioned, parts of the toolbar in firefox or the desktop
appear. I running an upto date ports/source etc on a 7.1-PreRelease