-For acceding in the menu you must select preferences then go to "user interface" and untick "activate window personalisation", restart jdownloader for seeing the change.

-For quitting normally the program (by clicking in the top right cross), you must go to extension manager in preferences menu and disable "JD notification zone" since hildon doesn't handle minimizing applications in the status bar, disable also JD unrar because it is x86 version of unrar.

You have now (almost) fully working JDownloader on your N900

I can confirm after days of use that it is a bit heavy for the N900 but definitively working great and usable