Hi, I'm the author of the post. I've been using JDownloader on Linux for years and never noticed a problem with Adware. Can you please elaborate? I'd really like to know more.
It seems to occur only using the web-installer, which is the one you're offically prompted at by the creators of JDownloader.
Well, I removed JDownloader and manually fixed the start page and search engines of firefox to remove the sweet-page stuff, but somehow my firefox is still screwed.
Questionable decision by the maker of JDownloader. I can't imagine that the money he gets for this is worth the damaged reputation.
Edit: I just ran an adware scanner. Besides the Sweet Page stuff, WindowsManagerProtect and Hold Page was installed. Several Registry Entries and Firefox setting were infected. Unbelievable ...
Since you didn't give alternatives, allow me: the program you should use is called quvi. It comes with a large number of scripts for extracting videos from sites and you can easily write more or patch existing ones, since they're all written in lua.
Also, a while ago I was working on making JDownloader less terrible (it should work like wget, UNIX philosophy and all). It's very labor-intensive though, but I may continue if enough people are interested (or help out): https://github.com/espes/jdget