Ubuntu file attachment dialog in Thunderbird doesn't allow referencing network shares

[David M. Karr]

I've noticed that when trying to attach a file in Thunderbird, the 
Ubuntu file dialog that comes up doesn't have in the "Places" list the 
"Network", which makes it impossible (as far as I can tell) to attach 
files from a network share.  This could be a purely Thunderbird problem, 
but as it brings up a native Ubuntu file browser dialog, perhaps not.

Every time I've needed to attach files that lie on the network 
somewhere, I first have to copy them to my local drive, and then attach 
them from there.

Is this intended?