OK, I was able to fix that.

about:config->browser.download.alwaysOpenPanel toggle to false

I have the same problem. I've tried changing browser.download.panel.shown to false but every time I download something it changes itself to true. I also tried changing browser.download.alwaysOpenPanel to false but browser.download.panel.shown still changes itself to true even then. Any solution?

ok. this is weird. so whenever I tried changing the about:config settings I got the download panel to show up again on the next download but since I changed browser.download.alwaysOpenPanel it only opened it once and every subsequent download didnt open it. so of course I thought it didnt work when the panel opened after I changed it. so if you have this issue, just change browser.download.alwaysOpenPanel to false and you'll get the panel one time but its gone again after that.

OK, I was able to fix that. about:config->browser.download.alwaysOpenPanel toggle to false

Thanks for letting us know that you fixed the problem. I'll mark this question as solved.

For the record, here's the report for the bug that was fixed by adding this new preference: Bug 1738372 Want to be able to disable the download panel opening for each download. _{Please read Bugzilla Etiquette before posting comments in bug reports.}