Bug 1041372 - [User Story] Rocketbar behavior for fullscreen apps with navigation chrome

https://bugzilla.mozilla.org/show_bug.cgi?id=1041372
I'm a bit worried about all the app specifics changes with the maximized class. This is going to create some reflows during the expand/collapse animation.

I wonder if the new collapsible class, instead of scrollable in bug 1058637 may help to minimize the issue and avoid changing display/dimensions.