[Trisquel-users] Why does Trisquel have thunderbird in the repositories, as opposed to icedove?

[christian]

My understanding was that the reason firefox was rebranded to Abroswer was  
that the links to non-free extensions were considered an implicit endorsement  
of non-free software.  I do trust that Trisquel would use icedove or another  
rebrand if the fsf was not okay with thunderbird, but could someone clear up  
my confusion on what makes something acceptable to be included in a  
fully-free distribution?  Sorry if this is a stupid question.  I actually use  
thunderbird btw.