The only AES text encryption that works (consistently) well across multiple platfroms! Rated 5 out of 5 stars

it works very well In several web-browsers; Firefox, Thunderbird, SeaMonkey, Opera, and Google Chrome!
Also, has an Lock The Text Online Edition at:
Use the "Lock The Text Online" page to lock or unlock your text, any time, any where.

Also, you can find a "Lock The Text Offline Edition" at
It is a single HTML file which a user can download, save and then open locally. The file at SourceForge has all the Online Edition files(HTML, CSS, Javascript) in one file and user doesn't even need the internet connection to run it.

It is a simple AES text encryption and easy to use Firefox add-on!

This user has a previous review of this add-on.