Tenfourfox advises us that there are security issues with bad SSL certificates getting into the wild in F/F 6.
Mozilla has decided to release a 6.0.1 chemspill due to a nasty issue with more fraudulent SSL certificates being issued through a compromised certificate authority (DigiNotar).
There will be a patch version of F/F 6 due shortly to close this security loophole. More soon.
UPDATE: See this later post about Firefox 7 for PPC Apples.