In Youku's HTML5 player, fullscreen doesn't work as expected when unprefixed Fullscreen API is enabled. It is currently unclear what is happening in this case, but we would need to investigate this in order to ship the unprefixed API.

Version 59.0a1 Build ID 20171213100213 User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0 At this version, clicking full screen button and it will exit fullscreen mode immediately. link: http://v.youku.com/v_show/id_XMzIyNTc5MTU4NA==.html?spm=a2hww.20027244.m_250379.5~1~3!5~A&from=s1.8-1-1.1

I have the same issue, and mozregress tells me 2016-05-11 is good but 2016-05-12 is bad. However Firefox 57 (release version) is good too.

Release version is good because unprefixed Fullscreen API is disabled on release version. We would need to investigate how the unprefixed API interacts with their frontend code.

Is there any progress in this issue? Or when will full-screen-api.unprefix.enabled come to true as default in release version.

miketaylr analyzed this problem in bug 1440921 comment 6 and it seems this is a problem in Youku that they have some logic issue when document.fullscreen is exposed. Since these two are basically the same issue, and there is more context in that bug, duping this into that bug.