Filechooser different behaviour between Iceweasel and Icedove


My mother noticed something interesting on her laptop (squeeze).

When trying to attach a picture in a Gmail using the webinterface (via
Iceweasel) a click on the file will show a preview in the filechooser
(somewhere on the right side of the files list).

When trying to attach a picture while composing a message in Icedove,
(what seems to be) the same filechooser does not show a preview.

If it matters I can reproduce it on my sid system.

Any idea where's the difference and what I can do to get the picture
preview via Icedove?

Kind regards,
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