According to our plan for M2 , we have some steps for CSS Transitions: 1. Detect new transitions and check we get the right values out 2. Remove animation styles when generating transitions i.e. the "after-change style" 3. Bringing animations up-to-date and not generating transitions as a result 4. Making sure transitions on descendants with different transition-duration trigger correctly. This bug is for the step 1: Detect new transitions and check we get the right values out. However, we still have some thread-safe issues in Bug 1340938, so we might just try to let it run, and then fix those thread safe issues later, or wait for part of those issues are fixed?  https://public.etherpad-mozilla.org/p/stylo-animation
Promote to P1 because I think it's better to finish this before Taipei work week. (So we can know how many thing we need to discuss for animations/transitions)
Now Brian has been trying to modify the transition spec, especially triggering conditioins in bug 1192592.
(In reply to Hiroyuki Ikezoe (:hiro) from comment #2) > Now Brian has been trying to modify the transition spec, especially > triggering conditioins in bug 1192592. Thanks!. Transitions is soooo complicated.
I think we should probably do (3) first -- i.e. the animation-only restyle.
(In reply to Brian Birtles (:birtles) from comment #4) > I think we should probably do (3) first -- i.e. the animation-only restyle. FWIW, I did put a link of a try for the bug what I am working on implementing the animation-only restyle. Bug 1344966 comment 2.