The toolbar style in sidebar.css shouldn't set its display to block. It should just inherit the display attribute from xul.css. Removing that line will allow sidebar toolbars to collapse again. This is really really easy to fix, might as well get it in for M5.
Set milestone to M5.
I have a fix for this
elig, can you verify?
i can verify. doing so.
Moving all Apprunner bugs past and present to Other component temporarily whilst don and I set correct component. Apprunner component will be deleted/retired shortly.