Created attachment 337698 [details]
Suppose there are two serial animations called A & B in one page. When user clicks a link to open a new page in the same tab and then press back button of safari (both iOS and macOS), the previous page are opened again. At the time, the B animation runs again.
Here is the demo to reproduce the bug: https://gist.github.com/599316527/475ae4e0686834d2852419b81c39ddf0