40.0更新内容：
New
- Android Presentation API for screen casting
- Download protection from potentially unwanted software
- Long press back/forward nav buttons in app menu brings up history list
- Smoother, more reliable CSS animations via asynchronous animations
- JPEG images use less memory when scaled and can be painted faster
HTML5
- Support for new Unicode 8.0 skin tone emoji
- IndexedDB transactions now non-durable by default
- Implemented AudioBufferSourceNode.detune to modulate playback rate in cents
直达链接：Firefox Beta 40.0