The old Firefox 3.5.19 branch has been EOL since April and is inscure now. Instead of downgrading to a old insecure version perhaps you could try this User Agent Switcher extension to fool the site into thinking you are using Firefox 3.5.19 and not 5.0 as Ancestry should really update their browser sniffing if they suggest Firefox 3.5.* as the most current version to use over 5.0 or even 3.6.* or 4.0.1 User Agent Switcher extension https://addons.mozilla.org/en-US/firefox/addon/user-agent-switcher/ If you really want to still take your chance with 3.5.19 then see ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/3.5.19/mac/ and pick your language.

Thanks very much I'll check this out. Crawford