If you are running Jalview 2.10.0 under Ubuntu or some other (possibly GTK based) Linux desktop, you may find that after opening the Sequence Fetcher, you are presented with a dialog box just showing 'OK' and 'Cancel' buttons, but nothing much else. The empty panel is due to an underlying problem with Java, but you can still choose from the list of databases with the keyboard !
There are six databases provided by default in 2.10.0: EMBL, EMBL (CDS), Ensembl, Ensembl Genomes, PDB, and Uniprot. Press the Up or Down arrow keys to select between these, and a message in the dialog box will show which database you have moved to. You can also type the first letter to jump to a particular database. Once you've made your selection, you'll need to click the 'OK' button to proceed to that database's fetcher dialog.