Facebook's content can be rendered with a free software browser (such as
Trisquel's Abrowser). The mobile version of Facebook does not make this
browser run proprietary Javascript. So, unless you prove the contrary,
"Facebook can be used with 100% free software".
Facebook's main use is to distribute content and communicate with other
users. It is not doing one's own computing. It is not SaaSS.
Again, I am talking about the main use of Facebook. Facebook's Flash "apps"
(that only run in a proprietary Flash player) and are about solo games
(SaaSS) contradict both points but are not Facebook's main use.
Facebook's problem is that it infringes its users privacy. It has even become
a threat to humanity that is as huge as its database (that is now known to be
shared with the NSA). I do not like Facebook. At all. But that is not a
reason to lie about it and pretend that it cannot be used with free software
or that it is SaaSS. That is not intellectually honest. We are to convince
people not to use Facebook for the right ethical problems it raises.
