A smart user backs up her profile. This can be done by simply copying the profile or, even better, using the MozBackup program.
Keeping a copy of the installation package on your computer makes reinstalling Firefox much easier.
There is no reason not to be able to use both Firefox and Internet Explorer together. Even though only one can be the default browser, the other is still usable.
All your personal settings are stored in the Firefox profile. If the profile becomes corrupted, it can cause Firefox to fail to run.
The Firefox Profile Manager enables you to create new profiles.
Under Windows XP and Windows 2000, each user has her own profile. This allows customization of Firefox on shared computers. Firefox always loads the correct profile for the user.