Welcome to Linux.
In Linux, we do not typically update our applications one-by-one by downloading them from various websites. (I call that flawed method "The Windows Way.") Instead, we use a "package manager" that installs packages from a central "repository" of tested and trusted software.
In Fedora, the package manager is called "yum" and you can bring your system up to date with:
That will update all applications, including Firefox, to the latest versions.
This is assuming of course that you are using the latest Fedora 14 (which is my recommendation if you are the kind of person who always wants the latest and greatest).