Please use a Google Chrome extension instead of the bookmarklet from this video. Bookmarklet version will be deprecated in the future.
This google chrome extension can be used with any web page by clicking on "Encipher it" button. It ask for the password, generate secure key and encrypt or decrypt the text on the web page. Optionally, it can save encrypted text on the external server and provide short link for access.
The plain text and the key is managed inside browser memory and never passed by network.
However, if you are using online version or the bookmarklet, the encryption code is loaded from the server. Be aware of man-in-the-middle and phising attacks. For safe use, ensure that site address is exactly https://encipher.it ("https" important!). If you see red alert, please stop using this site and contact support.