Confirming this bug still exists.

["Dan Merillat" <dan merillat gmail com>]

I'm going to take a look into it, here's what I see so far:

using focus-follows-mouse, click 'write' in thunderbird.  Place the
mouse directly _UNDER_ the To: text field, and press any character.
The address completion window pops up, then instantly closes, chosing
the first completion and pasting into the text field.   Placing the
mouse anywhere where it will not intersect with the text window will
not cause this behavior.

A similar problem happens with firefox/mozilla suite URL completion -
if I type quickly, focus bounces around and characters drop.  Having
to slow my typing down to a hunt-and-peck speed is extremely
obnoxious.

I'm not positive, but it looks like if a child window opens under the
cursor, it gets a focus _AND_ click event.   I'm going to do some
event tracing to see what I can find.