71e635d22e
After bug 306344 this is the last remaining incompatibility with <marquee>. I think we should be able to drop it. Use counters for "finish" are relatively high (>0.1%), but I'm pretty sure that's because that event name is shared with web animations. "bounce" is a more realistic measure, and that's 0.003%, which is more expected. Differential Revision: https://phabricator.services.mozilla.com/D206387