Update/Warning: This extension doesn’t work with Epiphany-Webkit. I’m sill trying to figure out the way to write a new extension for the new Epiphany. More information will follow soon.
If you are having problems downloading videos with video downloader, this is likely bug 583616 biting you. Whenever the preference dialog of epiphany is opened the download path is reset to ‚/‘. As a result you get instant download completed without the video being anywhere. To temporary fix this reset the download path in the preferences (if you need instructions: Look in the middle of the third paragraph of this blog post).
I’ll use this opportunity to point out two hidden feature. If you middle click on the video icon, it will open the video in a new tab. With the totem-plugin installed (and it recognises that it can play it) it might play the video right there. Otherwise you will get the well-known dialog box asking for a "save-as" or "open". Thanks to Josselin Mouette for this patch.
It is possible to play the videos in totem instead of downloading (this was requested in bug 567801). However I don’t have any UI (not even gconf) to switch it on, yet. So you’ll have to change
DEFAULT_OPEN = OPEN_WITH_DOWNLOAD to
DEFAULT_OPEN = OPEN_WITH_TOTEM in video-downloader.py. Tell me what you think about it. I’m thinking about making it the default as the first bug cripples the automatically downloading the video. On the other hand it takes a bit for totem to start playing and after all it is called “video downloader”.