This documentation applies for JabRef 3.8.1 or later.
To use this feature, choose BibTeX → New entry…. In the lower part, there is the box “ID-based entry generator”. In the field “ID type”, you can select “Title”. The field “ID” is focused. Enter the title here and press Enter to generate an entry based on the title. You can also click on “Generate”. Then, http://dx.doi.org/ (provided by http://crossref.org/) is used to determine the DOI and convert the determined DOI to a BibTeX entry. The found entry is opened in an entry editor. In case an error occurs, a popup is shown. In case no DOI could be determined, no entry is created.