Disabling Dropbox must be done from your Dropbox account.
Log into your Dropbox account
Go to your Dropbox Account Settings
Click on the Security Tab
Scroll down to the Apps linked section
Click the "x" to to right of where it says FastBound
Choose whether or not to keep the files in the FastBound folder
Click the "Uninstall" button
There will be a "App uninstalled correctly" message at the top of your browser
To verify Dropbox was disconnected login to your FastBound account and go to Settings > Dropbox and you will see the message "Reconnect required"