I have yet to be dissatisfied with the one and only Video DownloadHelper for Firefox. Almost nothing else is worth dealing with. (Tragically, there seems to be no equivalent for Chrome.)https://addons.mozilla.org/en-US/firefo ... oadhelper/
One alternative are the various Cache view utilities from http://www.nirsoft.net
, which will let you find the precise URL of an embedded video file and download it as you see fit. (In theory, it can be used to copy files out of the cache that have finished buffering completely, too, but I haven't had much luck with that.)
But the tricky things that cannot be downloaded with DownloadHelper and its ilk are those videos that stream directly off a website and are not stored in a browser cache. For these, Nirsoft offers WebVideoCap
, which basically reconstructs the video from network packets. It does not support RTMP, however; I'm pretty sure there's some other utility that does – I just keep forgetting what it is.