New Features:

• OpenH264 support (sandboxed)
• Search suggestions on the Firefox Start (about:home) and new tab (about:newtab) pages
• Windows: OMTC enabled by default
• New CSP (Content Security Policy) backend
• Support for connecting to HTTP proxy over HTTPS
• Azerbaijani [az] locale added
• Cubic-bezier curves editor
• Display which elements have listeners attached
• New sidebar which displays a list of shortcuts to every @media rule in the current stylesheet
• Paint flashing for browser content repaints
• Editable @keyframes rules in the Rules section of the Inspector
• CSS transform highlighter in the style-inspector
• @counter-style rule from CSS3 Counter Styles specification implemented
• DOMMatrix interface implemented

Feature Improvements:

• Proprietary window.crypto properties/functions removed
• JSD (JavaScript Debugger Service) removed in favor of the Debugger interface
• Improved reliability of the session restoration
•  Improved search experience through the location bar
• Slimmer and faster JavaScript strings

Fixed Issues:

• Fix incomplete downloads being marked as complete by detecting broken HTTP1.1 transfers 
• Various security fixes