There was a 5.0, 5.0.1, and also a 3.5, but there was never a Firefox 5.5. The only other thing I can think of that might've been misconstrued as 5.5 would be the 5th beta release for 5.0, 5.0b5, but nobody should be using that. In any case, they're all available on the FTP server so you should be able to find what you need there: * ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/