I've been using "Torch Browser" which has a built in one click function to leech videos from various sources... It's a clone of Chrome, but adds a few little niceties...

However, I think many websites are getting wise to this, and for example, it (the one-click feature) doesn't work anymore on about 90% of YouTube, Pornhub or XHamster... seems to mostly still work with XVideos and YouPorn, but for how much longer is anyone's guess...

Any newer suggestions...?