This extension is an absolute gem if you run a middle school computer lab. It basically locks the browsers settings, tools, and preferences so that they cannot be accessed unless a password it supplied.
Here are the features I like the most from this tool:
-The homepage for the browser cannot be changed by students.
-Certain filetypes, i.e. .exe .zip .mp3, etc, will prompt the user
for a password prior to download.
-All bookmarks, network settings, and themes are password locked.
We've been using this extension for almost an entire school year at the time of this posting and the browsers
remain unchanged. It's really a great classroom tool.