The simple answer is Portable Firefox which allows you to enjoy your favorite web browser from any Mac whether or not it's installed and without having to install anything new. Firefox Portable fits on a portable USB stick so you can take it anywhere as long as the Mac your using has a USB slot spare.
There isn't a great deal of difference between Portable Firefox and the main version but it has been optimized slightly to allow faster browsing, extension compatibility and it includes a more prominent navigation history. Even though it's portable, it can still store passwords for you so you don't have to mess around filling them in all the time.
For die hard Firefox fans that simply can't bear to be aware from their favorite browser, Portable Firefox is the simple solution.