The first version of FlashVideoReplacer is available for download through the Development Channel. Only YouTube, Vimeo and Blip.tv are currently supported, but you can suggest other sites to be included in the compatible list by voting on the poll above. If the site is not included in the poll, then please send me an e-mail or fill a feature request at the project Bug Tracker.
Since the extension is under development, it won't be approved immediately by Mozilla editors. It takes about 3 weeks to be reviewed. This means, until the extensions is approved, it won't update automatically by Firefox add-on manager. So I strongly recommend that you subscribe to the extension RSS feed or Twitter, in order to receive news about updates. Due to the nature of this extension, I'm predicting will be constantly updated, to include new supported sites and to fix issues due to web site changes.