Thunderbird no longer sees network shares for attachments (Ubuntu)

After the update to version 52.1.1 (64bit) on Ubuntu 16.04 the file dialogue to attach documents no longer shows any network shares. Neither does it show an obvious way to include them. It does show the local shortcuts from Nautilus and a general "Other locations" which accesses the local file system, but no network. I have about ten different network shares to link to and pull attachments from, so this is a really big inconvenience. Screenshot is in German. (And apparently fails to upload at all... Seems to be loading up forever)