The issue with the animation is that it removes the composebox div
when it's done -- or more relevantly, it "adds" it when the composebox
appears, which causes some DOM elements to get reshuffled slightly
which causes some jitter.
(Similar to what was happening with the email addresses earlier.)
So instead of using display:none, we play with visibility:hidden,
which causes the thing not to show up, but doesn't cause it to
lose its place in the DOM.
(imported from commit a18dbdcd1784b2b54436d48d8425d5fdc8dfbba4)
This is a regression introduced by switching from links to buttons,
which get blurred by hide_compose.
(imported from commit f5aa67cb949f3edc7f86a0ef0d7f48b43860138b)
I would like to have split this into several commits, but it's hard to do
incrementally, because functions need to be defined before their use in global
data.
(imported from commit 31533396b236f3b657950b073982c317256f082a)
