Firefox Mobile (Fennec) has also desktop builds. They are very useful for mobile web site testing as the browser is fast, has real keyboard and is only one mouse click away.
Here are instructions how to run Firefox Mobile on Ubuntu Linux (tested on 32-bit Ubuntu 10.10)
wget http://releases.mozilla.org/pub/mozilla.org/mobile/releases/latest/linux-i686/fennec-5.0.en-US.linux-i686.tar.bz2 tar -xjf fennec-5.0.en-US.linux-i686.tar.bz2 cd fennec ./fennec
.. and thats all you need. It works out of the box! 400x times faster than using Android emulator browser.
There are also OSX and Windows builds available.