If you resize the window panes in Messenger, you get all kinds of video artifacts. Problem is reproducable.

This is really a layout bug introduced shortly before M9. I see it all the time too. Lisa, I'm going to try to hit you up for your bug knowledge, can you dig up the original bug for this so we can mark it as a duplicate? Of course I'm giving you a vague description of the bug so consider this a challenge =). Thanks!

Ok, I will try to hunt up the other bug a little later today.

Is this the bug you're thinking about, Scott? http://bugzilla.mozilla.org/show_bug.cgi?id=11478

Re-assigning to putterman because he's been all over this problem. That's what he gets for stopping by my cube and telling me what he's working on =).

I just checked in the fix.

Build 1999092409M11: Win32/NT4, Linux/Redhat 6.0, Mac 8.5.1 Verified Fixed. I used the divider bar (aka splitter, grippy) to resize the left pane and it resized and displayed as expected.