Please support transitions to auto values. Like a transition from height: 0; to height: auto;
I attached such a non-yet-working example.
See also Mozilla's Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=571344
The way this works now seems like a bug.
A transition from a specific height to height:auto will result in the element animating to height:0 and only then jumping down immediately to height:auto.
A transition from a specific height to height:auto should result in a smooth transition to the value calculated by height:auto. The height:auto calculation shouldn't occur after the transition.
Tested with WebKit nightly (r97312) and test suite,
The 5th test, which corresponds to this bug report:
...the initial value of an animated property is 'auto'
I expect the property to be animated properly."
passed, so this bug is resolved at or before r97312.
Marking this as resolved. Although the current behaviour may not seem ideal, the specification (http://dev.w3.org/csswg/css3-transitions/) doesn't deal with what happens when animating to/from auto at all. It's better to discuss this issue on email@example.com and wait for a specified behaviour to exist than to debate in this bug.