I'm running win7, and after updating from jabref v2.5 to v2.6, I lost the drag and drop functionality for adding new entries and also adding pdf files to existing entries. I've been very happy with 2.5 so I'll revert, but wanted to let you know. Thanks for the great software.
Could you provide more details? What did you drop where?
Here, dropping a PDF onto an antry and onto the preview works.
Dropping a .bib file leads to opening it. Do you expect something else?
Dropping a text containing an entry leads to addition of that entry (via the import dialog).
I don't miss anything. What do you miss?