Comment 12 for bug 304345

I also face this issue.
I would expect the file chooser dialog to allow me to access network bookmarks (including mounting them if they are not mounted already).
It's very annoying when you want to save a file on a network share from Firefox or Thunderbird : you have to save it locally, then transfer it with nautilus.

I found the following workarounds :
- mount permanently the network locations in /etc/fstab : it works, but is not adapted to all situations. In my case, the server that hosts the network share is a standard PC, not a 24/7 server. So, if this PC is not up at startup time, the share is not mounted
- add a bookmark for ~/.gvfs directory, as suggested by smonff : it appears in the file chooser, but is empty if the share is not mounted. So you have to mount it before
- add a bookmark for ~/.gvfs AND install/configure the package gigolo : this software can automatically mount network shares. If you declare it as a startup application, it will try to connect every minute. See http://www.borpin.co.uk/2011/03/29/map-network-drive-in-ubuntu-again/ . It's still a workaround but it's the best I found so far.

In any case, it would be much much easier to be able to open/save directly in a network bookmark.
It is a frequent use case at home or in small organizations (several computers with shares to exchange data, but no central server)