Changelog:

What’s New

NEW
When opening a new tab, users are now presented with their most visited pages
NEW
The default home page now has quicker access to bookmarks, history, settings, and more
CHANGED
SPDY protocol now enabled by default for faster browsing on supported sites
CHANGED
Restored background tabs are not loaded by default for faster startup
CHANGED
Smooth scrolling is now enabled by default
DEVELOPER
72 total improvements to Page Inspector, HTML panel, Style Inspector, Scratchpad and Style Editor
DEVELOPER
The column-fill CSS property has been implemented
DEVELOPER
Experimental support for ECMAScript 6 Map and Set objects has been implemented
DEVELOPER
Support for the CSS3 background-position property extended syntax has been added
DEVELOPER
The :invalid pseudo-class can now be applied to the element
DEVELOPER
The CSS turn <angle> unit is now supported

Known Issues

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
Some synaptic touch pads are unable to vertical scroll (see 622410)
UNRESOLVED
Windows: The use of Microsoft´s System Restore functionality shortly after updating Firefox may prevent future updates (see 730285)