It seems that Firefox binaries are covered by an end user license agreement that might even not allow redistribution and they contain proprietary code for error reporting: Talkback.
They are free to use any license they want. Who cares?!
Those who care about your freedom care.
Freedom also means to let people decide themselfes how they want to do things, not to tell them how they shall do it.
Freedom doesn't mean the freedom to reject freedom, or subjugate others into giving up their freedom. Non-free software is never a solution.
So yes, this is what the FSF (and others!) should do and has been doing for quite some time, presure people and companies into freeing users.