If you sometimes need to send large files as email attachments to friends and family, uploading them to emails is a tough work. It may take a lot of time if you are on a slow connection, and chances are that your email provider may just not accept large files.
To overcome this, Thunderbird added the Filelink feature through which you can upload your files to a cloud service and send the file link as email. From Thunderbird 15, Ubuntu One has been added as a cloud provider, so you can use your Ubuntu account to send attachments through Thunderbird on the file.
To activate this, update Thunderbird and go to Edit menu and click on Preferences. Select Attachments tab → Outgoing and Add Ubuntu one as a Filelink provider.