Firefox 19 isn't going to officially launch until tomorrow, but you can get your hands on the latest version of Mozilla's browser for Windows, Mac and Linux right now.
You can download it directly from Mozilla's FTP server, or you can wait until the official launch and continue to check the Firefox website. Mozilla's blog also provides information about the release if it's significant enough, like Firefox 19. If you are using Firefox as your mobile browser, you might want to also keep an eye on the Google Play Store, too, as it should launch for Android tomorrow.
Further Reading: Read and find more Internet Browsers news at our Internet Browsers news index page.