Add "DownloadPanelTweaker:ToggleDownloadSidebar" API event
Example for OmniSidebar:
window.addEventListener("DownloadPanelTweaker:ToggleDownloadSidebar", function(e) {
	e.preventDefault();
	toggleSidebar("viewDmgrPlacesSidebar");
}, false);
Support for download sidebars from OmniSidebar and All-in-One Sidebar