In order to keep yourself from having to activate the dangerous Flash in your browser, you should always download web videos to your hard drive and play them from there. This also saves you the additional data traffic which would be needed to view a streaming video again. JonDoFox contains some download tools for doing this. For Windows and Linux (under WINE), there moreover exists an excellent freeware program called aTube Catcher. You may configure this program for JonDo by activating the HTTP proxy in aTube Catcher under Tools->Connection settings and setting it to Host:127.0.0.1 and Port: 4001

For playing movies of all video formats and on all operating systems, the free VideoLAN Media Player is a very good choice.