Ah welcome to firefox! You should be able to go to the help tab and just click on check for updates to get FF3. If that doesn't work just download it and install.
Firefox web browser | Faster, more secure, & customizable I would suggest this as an add on its great. It blocks anything that starts in flash from playing. If you want to see what it is then click on it and the flash item will start like normal.
https://addons.mozilla.org/en-US/firefox/addon/433