New Async drawing model for plugins: https://wiki.mozilla.org/NPAPI:AsyncDrawing - RESOLVED FIXED: https://bugzilla.mozilla.org/show_bug.cgi?id=651192
Fixed an important WebGL regression (performance) introduced in Firefox 12 (Aurora) http://bugzil.la/724476
The arrow keys now scroll three lines at a time instead of two:
http://bugzil.la/725700
FIXED: http://bugzil.la/699565 - JS: Implement Harmony for-of loops. https://developer.mozilla.org/en/JavaScript/Reference/Statements/for...of
FIXED http://bugzil.la/720208 - DOM4 DOMException types and codes implemented.
Snappy optimizations for faster Firefox startup on Windows: http://www.brianbondy.com/blog/id/127/
Plugin processes killed after three minutes of not being used (please read http://bugzil.la/501485 before firing questions)
FIXED http://bugzil.la/720258 - Inline autocomplete only autocomplete URLs you've typed
FIXED http://bugzil.la/674370 - OSX 10.7 Support animation when opening windows in Lion
Support for different values for X & Y directions (two-value syntax) has been added to CSS background-repeat : https://developer.mozilla.org/en/CSS/background-repeat
"Copy Link Location" added to the links' contextual menu on View Source. http://firefoxnightly.tumblr.com/post/18324014797/on-view-source-the-copy-link-location-entry-has
The new live bookmarks landed! Now it is wholly async (no IO on main thread) and have a read icon. Fx is more snappy. https://bugzilla.mozilla.org/show_bug.cgi?id=613588
Support of the 4-value syntax has been added to CSS background-position. https://bugzilla.mozilla.org/show_bug.cgi?id=522607 CSS type
is now wholly supported.
SPDY testing on trunk is going well.We are not planning to turn it off (may ship with it on in Firefox 13) unless something serious comes up
Source:- Firefox Nightly twitter channel