Tried uninstalling FlashGet. Even without it I have the same problem. And the same also with Orbit. Reinstalling FlashGet didn't make any difference.
The string "flashgot.dmsopts.JDownloader.url" doesn't even exist in my about:config.
bug since 1.1.9.8
Re: bug since 1.1.9.8
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1) Gecko/20090624 Firefox/3.5 (.NET CLR 3.5.30729)