The height of the subview being opened was supposedly calculated using an off-screen container independent from the currently displayed views, but this didn't work as expected because of the incorrect box alignment. This is now fixed and the correct minimum and maximum heights are set on the container separately, also preventing the current view from flickering before the transition in case the subview was taller.
With this issue fixed, the height can now be recalculated each time the subview is opened, without the caching that caused incorrect results when the same view was reopened with different elements or text.
Jumping could also occur because of a border applied only during the transition, which could influence the subview height in the presence of wrapping text.
MozReview-Commit-ID: EWHs1hFKXT4
756cb221b2