Before you all write and tell me, yes, I know the build says b13pre. That's because there was a last-minute security bug that landed and by the time I jumped on it, the build milestone had already been advanced. There's no real purpose in a checkin-and-out to simply massage the version number in a beta, so I left it as was. However, despite the version number, this is beta 12.
Okay, enough of that. Beta 12 has several new features and these are mostly good, some strongly so. First of all, the most visible change is that the hovered URL in the location bar is gone, as threatened, replaced by a Chrome-like strip at the bottom (the same one used to report network activity). I kind of miss the location bar layout, but I adapted back to the old style very quickly. The bar will move to the other side if you hover over it, so it doesn't get in the way. Second, there are small subtle changes (again) in tabs, including the close button, which is now just a tiny grey X in the default theme. The bogus new change is that the content-specific modal dialogue boxes are now super blah (I liked the quasi-Aqua ones in beta 11 better -- these are boring).
Mozilla also made some significant changes to the plugin architecture on Mac, as I warned you about. I was able to hack around them (I think), but the time is coming when I might not able to. Flash performance seems slightly worse because of the changes (which favour CoreAnimation and hardware acceleration), but it's hard to get accurate metrics. I still advise downloading such videos to disk with any of the available video site/YouTube extensions and playing them outside of the browser.
Specific to TenFourFox, we have a few fixes landed in this release for a new problem and for a couple old ones. One of our oldest and most frustrating bugs was the awesome bar refusing to suggest anymore when you typed a totally novel URL it could not suggest for: when the box closed, it would not open again (though it could still receive keyboard events). I'm inclined to chalk this up to 10.4 being a brat who can't stand not knowing the answer, because I could not find a specific cause, and tweaks to the underlying object had side effects for other auto-complete objects. So, if you can't fix the cause, remove the situation. Starting now, if you type a new URL that the awesome bar doesn't know, rather than simply closing, it just shows a single blank box (actually a single blank stub suggestion). This works with the interface, and the awesome bar works normally. If someone else has a better idea, say so, or send me source code. :P
I'll post later this week or early next what will happen for the final formal release. Until then, enjoy beta 12.