How can I add a dropbox folder option under my "Places" in Nautilus

There multiple alternative options:

Pressing Ctrl+D adds a bookmark to the folder you're in (tested under Ubuntu 12.04 & 13.04). For Ubuntu 14.04, use the Files application (a. k. a. Nautilus) to navigate to the folder you want bookmarked, then press Ctrl+D, the same with going to the top menu bar and selecting Bookmarks → Bookmark this location.
Select the folder that you want added to bookmarks, then go to the top menu bar and select Bookmarks → Add Bookmark.
You can add them editing by ~/.gtk-bookmarks. Say you want to add ~/Software and ~/Ebooks folder under Places. Just add the following line at the end of ~/.gtk-bookmarks:
```
file:///home/my_username/Software  
file:///home/my_username/Ebooks    
```

Try it out and let me know. Hope it helps.

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