The changes I like:
Private and Secure: Do Not Track: (...) allows users to opt-out of tracking used for behavioral advertising.The HSTS and CSP still needs some implementation in the webservers (upgrading,etc..) but I think that will happen very fast.
Firefox (..) fix(...) flaws in some Web standards to prevent others from accessing your browser history.
HTTP Strict Transport Security (HSTS): automatically establishes secure connections to stop “man in the middle” attacks and keep sensitive data safe from interception during the log-in process.
Content Security Policy (CSP): prevent cross-scripting attacks by allowing sites to explicitly tell the browser which content is legitimate.
Some HTML5 support . It's still not a final standard but it's adoption is growing (some features more than others) and the features are already being used to great advantages.
And most visual/operational change: Tabs on Top! (you can change to the previous Tabs position if you like)
Now Opera, Chrome and Firefox looks very similar :-)
Changes I need some time to get use to:
Link Url information
It's my browser for choice!