Web Search can be done in JabRef by invoking Search -> Web Search. I chose Google Scholar and no matter which paper title I searched, I got empty result!
This feature seems to be broken in older versions of JabRef. This is a known bug as reported here. I had installed JabRef v2.10b2 from Ubuntu archives.
I removed this and installed the latest v3.0 and Web Search worked fine in it.
Tried with: Ubuntu 14.04