If you've been using Google Chrome, you'll notice that the proposed Firefox 4.0 seems to be trying to "emulate" their design--especially with the top portion; this is a testament to Google's design team.
Some of you may ask, is this or a bad thing for Firefox? It may not seem to look good because they copied Google's design, but in the end with their extensive add-ons (admittedly Google Chrome's current weakness), some of their old users MAY go back.
They just need to sort out on the low speed and memory-hogness of FF and they just may cement their position on the top.