This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
Returns the time, in milliseconds since the epoch, at which animations started now should be considered to have started. This value should be used instead of, for example,
Date.now(), because this value will be the same for all animations started in this window during this refresh interval, allowing them to remain in sync with one another.
time = window.mozAnimationStartTime;
timeis the time in milliseconds since the epoch at which animations for the current window should be considered to have started.
Not part of specification.