What’s New

NEW
Silent, background updates
NEW
Support for SPDY networking protocol v3
NEW
WebGL enhancements, including compressed textures for better performance
NEW
Localization in Maithili (see all available locales)
CHANGED
Optimized memory usage for add-ons
DEVELOPER
JavaScript debugger integrated into developer tools
DEVELOPER
New layout view added to Inspector
DEVELOPER
High precision event timer implemented
DEVELOPER
The CSS word-break property has been implemented.
DEVELOPER
New responsive design tool allows web developers to switch between desktop and mobile views of sites
HTML5
Native support for the Opus audio codec added
HTML5
The and elements now support the played attribute
HTML5
The element now supports the media attribute
FIXED
Focus rings keep growing when repeatedly tabbing through elements (720987)

Known Issues

Unresolved
Debugger breakpoints do not catch on page reload (see 783393)
Unresolved on v15 Resolved in v16
Unresolved
If you try to start Firefox using a locked profile, it will crash (see 573369)
Unresolved
For some users, scrolling in the main GMail window will be slower than usual (see 579260)
Unresolved
Windows: The use of Microsoft's System Restore functionality shortly after updating Firefox may prevent future updates (see 730285)