Firefox's new features include automatic updates (users previously had to complete an installation for each update) and extra pop-up ad blocking.

FORBES: Magazine Article

In my tests on both machines, the actual installation took about two hours, but a full workday or more was spent tweaking each machine, and getting updates to Windows 8 and its built-in apps.

WSJ: A Review of Windows 8 Upgrade: Not for Old-at-Heart PCs