After Yoono Desktop Portable, here is Firefox Everywhere : a customized Firefox package which can be executed on any OS : Windows, Linux, MacOS and with a shared profile directory allowing you to travel with all your Firefox data on a usb stick!
Check out this surf session starting on Windows,
Then on Linux, 
And finally on a Mac! 
FirefoxEverywhere
Download:
- The Full edition (69MB) which works with all OS
- or the Windows only version (13MB)
- or the MacOs only version (26MB)
Tips:
- Don’t forget to properly disconnect your usb stick, or your profile may explode!
- This version is based on Firefox 3.6 branch in order to gain startup performance improvements of this incoming version! So don’t be afraid to have a browser named Namoroka instead of Firefox.
- On Windows, execute: launch-windows.exe
- On MacOS, launch-macos.command
- On Linux, either launch-linux-64.sh or launch-linux.sh(for 32bits)