This tool from the Firefox team let you send and upload with encrypt large files (up to 1GB) to share online.
This creates a link to pass along to whoever you want.
Just type send.firefox.com into the browser address bar and you will get an upload interface.
Each link created by Send will expire after 1 download or 24 hours, and all sent files will be automatically deleted from the Send server.
The Firefox Test Pilot send does not require an add-on, and can be used in any modern browser.