– improved memory handling
– bookmark and password changes now sync almost instantly when using Firefox Sync
– the “http://” URL prefix is now hidden by default (just like Chrome)
– the WebSocket protocol has been updated from version 7 to version 8
– fixed several security and stability issues
– added a system for users to send performance data back to Mozilla
Regarding that last one, Firefox will now collect data about your computer to help guide the Mozilla team as they work on newer versions. Concerned about privacy? Don’t be — it’s an opt-in system, disabled by default.