How did you get Javascript to work? As far as I know Metro apps cannot load or execute code dynamically (e.g. you can't use LoadLibrary or VirtualProtect). Are you using a Javascript interpreter rather than a JIT? Or are you using the Microsoft Javascript engine?
Firefox on android has felt very disappointing to me; I'm really interested in seeing whether this effort can do a little better to enhance the WP7 experience. (I use Android currently, may look to switch off, to which platform I don't know, in the next year or so)
Try the nightlies. I have no idea why on Earth they keep the stable build in the Market, it's god awful compared to the nightly builds. They're ... actually usable.
I can give you one good reason: they're unstable. Nightly crashes quite a lot on my phone, but Stable (and even Beta) are rock-solid. (Also, and this is just my opinion, the Stable interface is better than the Nightly interface. When it works, Nightly's a lot faster though.)
TFA says that the prototype is based on the Fennec (Firefox Mobile) XUL code. But since it's so early and so ugly, I expect the styling to become more Metro-y as development progresses.
Glad to hear that Firefox is looking at providing a Metro Themed browser (even if it's just to get away from IE), but looking at the icon set from the pictures, I think they are missing the boat on the Metro style.
The design work hasn't even started; this prototype is built with the same front-end code and theme as Firefox for Android. (Actually it's using a mish-mash of two different Android themes, because of a quirk in the way the prototype is built.)
The icons in the prototype were all designed for Android, and all will be replaced by real Windows/Metro icons in the final product.
[Usual discosure: I am a mobile Firefox developer.]
The rendering engine code is shared across all platforms (Android, Linux, Mac, Windows, etc.).
The "mobile" front-end code is currently used by Firefox for Android/Maemo/MeeGo. It's separate from the "desktop" front-end code used by Firefox on Windows/Mac/Linux.
To be fair, he did qualify it as a design in progress.
That said, I think standing out from the pack is far from the worst thing they could do. I love the live tiles idea, but the rigid design language gives everything a very "samey" look that I think could impact the usability of Start screens with lots of applications. How many one color icons will it take before they all start to look alike?
My comment was more on the actual nav bar and the icons contained within.
Especially for a browser, I really don't think that the nav bar is where you want to be standing out. Look and feel the way the user expects and get out of the way. Where the browser should be differentiating itself, is displaying web content as fast and as well as possible.
In terms of the look of the tile, I'm not entirely sure I agree with you, however I certainly don't feel strongly enough about it to argue.
This is an announcement that they finished porting it to the Metro environment, not that they finished their Metro version. There are more things to life than graphic design.