I cannot set up the link to DropBox from the Thunderbird preferences - attachments menu. The DropBox add-on is installed. When I click the ADD button in the attachments dialog box, another dialog box opens and allows me to select DropBox for my on-line storage. When I select DropBox, another dialog window opens and asks me to register. When I register my username and password and click on SIGN IN, nothing happens. The SIGN IN button appears to be inactive and does not link to anything. The dialog box remains open indefinitely until I cancel out and restart Thunderbird.

I have reinstalled Thunderbird from synaptic package manager, I have reinstalled it by downloading from Mozilla. I have confirmed my username and password with DropBox and my account is alive and well. I have reinstalled the DropBox for Filelink three times with no change in results. I attempted to set up on-line storage account with Box and had the same problem.