Screensharing allows remote viewing one computer by another one. Typically, screensharing software is downloaded onto a both computers in order to initiate a session. Many screensharing services allow the ability to control the host computer. The fact that screensharing allows one person to see and control someone else's entire computer presents privacy issues that we try to solve.
With Firefly you can only see the web page that the presenter is viewing. This provides a much more private, and secure sharing experience than other screensharing providers.