It would be great if Jabref allows to set the type of user field to "URL" so that double clicking on the URL opens the link in a browser (as it's already the case for the fields URL and Citeseerurl).
One solution would be to specify the type of the field in brackets behind the field name, e.g.:
General:crossref;keywords;file;doi;url;myurl[URL];citeseerurl;comment;owner;timestamp
Or you could assume that the type of the field is an URL if it's name ends with "url".
A third solution would be to determine URLs automatically by testing if the field's content starts with "http://".
So what would be the best solution? Maybe number 3.
Yes, I also badly need to type in multiple URLs, and also to have a special field for the URLs to various reviewing services, such as MathSciNet, Zentralblatt, ISI, etc.