It depends on how you uninstalled Firefox. If you used the default options when you uninstalled Firefox, all you have to do is download the setup file again from http://www.mozilla.com then run it to re-install Firefox. It will automatically pick up your user data such as bookmarks and passwords. The user data is not deleted if you use the default options when uninstalling Firefox. If you selected the option to "Remove my Firefox personal data" it will have deleted all of your user data such as bookmarks and passwords. In you did this you are unlikely to be able to recover the user data.