Greetings! Im a Firefox user from China Mainland, 3days ago I just had my Firefox updated to 66.0.0.3, then something went badly wrong. I just found HTML5 live streams from some some specific sites-----such as live.bilibili.com, keeps buffering when the stream is firstly opened, the only way to put things back together is pause/continue the stream, or swich to FLASH mode and then swich back to HTML5. This problem also happens when watching some other livestreams based on HTML5, and never happened in Firefox version 66.0.0.2. I wonder somthing went wrong with the latest ver, so I made this report. I tried 3 different devices,with 66.0.0.3 Firefox, and the problem happened on all of them, Im sure it's not my ISP caused the problem-----I tried with, and without Shadowsocks proxy. The sys environment: Windows 10 Professional 1709 Windows 7 Ultimate SP1 I browsed the Chinese communities, and found this is somehow a problem quite normal after the 66.0.0.3 update, a lot of users posted the problem but got NO response I updated the screenshot below.