Changes I've noticed:
-Spellcheck in text fields (YAY!)
-Different sound when it can't find something using ctrl+f
-"Extensions" and "Themes" are now grouped under one entry in "tools" – "Add-ons"

Hope they fix the copy & paste bug. I can pretty much forget my WIndows clipboard in combination with Firefox, unless I follow a specific ruleset:
- select text
- copy
- unselect text
- paste in Firefox address bar

When I do not unselect the text it won't work!