The domain name in the address bar is now highlighted, to make phishing more apparent — mimicking a similar feature already found in Internet Explorer — and Mozilla is claiming that there's some speed improvement. And that's about the extent of it.
However, for future versions, "A feature request calls for the removal of the version number from Firefox's "About" dialog."
How on earth do you file a decent bug report without the build number? That was something like page three of the first chapter of How We Test Software At Microsoft.
From Mozilla's own help article, "How to open a bug":
Make the Bug Summary useful
Which version of Firefox do you run? To know that, we need the "Build ID". Click "help" then "about Firefox/Minefield".
These guys are on a roll...