Mozilla have just released the first alpha version of Fennec: the mobile version of Firefox. At the moment Fennec can run only on Nokia N810 Internet Tablets; if you don't have such mobile, then you can always try Fennec in a Desktop environment. Fennec, even if still in alpha stage, supports:

• Bookmarks, including tags
• Smart URL bar ("awesome bar")
• Tabbed browsing with thumbnail images
• Integrated Web search - built into the URL bar
• Easy access to multiple search engines
• Zoom in and out
• Click on a phone number to initiate a call
• JavaScript API to get device location
• etc.

It's difficult to say now if Fennec will win the battle against Opera Mobile, Safari Mobile and others; for sure, the possibility to develop add-ons will help Fennec as it did for Firefox.
If you are still curios, you can see a video of Fennec.