I haven't used the menu or tool bars to visit files before, but I just
tried it and visiting worked, but modifying the directory list under
"Browse for other folders" didn't work. I started emacs -q and
clicked on the file icon in the toolbar or the corresponding menu bar
entry. At first I was able to add a directory to the list, but when I
tried to remove it, an error message window popped up which said:
"Could not remove a bookmark
Bookmark saving failed: Could not change file mode: waitpid() failed:
No child processes"
Then I tried to add another directory and this time it failed with the
same error message (except it said "Could not add a bookmark...").
Subseqently, even after starting emacs -q again, and even after
deleting ~/.gtk-bookmarks, no modification of the list has been
possible. As a sanity check, I tried the same in Firefox, which uses
the same GTK dialog, and it worked fine there. I don't know if it's
significant that, while testing the file dialog with emacs -q, I also
had an Emacs session with my initializations running (I first tried
the GTK file dialog there and found the same problems).