FSF is the idea of women being inherently superior to men or a society organised along the lines of extreme inequality of sexes with women holding all the power. It hinges on the idea that women, by the simple fact of being women, are inherently superior to men. In most such fantasies it's not actually all women - the women in FSF are usually powerful women, beautiful women, feminine women, real women - whatever that might mean. Still, the notion of superiority of one gender/sex over the other, or one group over another, is there. It assumes that the power given to the dominant in a power exchange game or relationship derives from some another characteristic, a characteristic shared by a whole group of people and one that either is or should be expressed in social hierarchies.
FSF is a simple inversion of the standard patriarchy which assumes that men are due a dominant position in society and relationships because of their inherent superiority. FSF doesn't kink on demolishing or subverting social hierarchies but on inverting them. FFS is Gor for the femdom-wired. Personally, I fetishise personal power exchange, and - just a little bit, y'know - subversion of social hierarchies.
But there is more to this than just the hierarchy stuff. I don't want to, even in fantasy, be submitted to because I am a woman. Dominance and femaleness are not the same thing and although I do believe that, on the mythical plane, there is some kind of ''female divine" archetype that's worth both exploring, playing and working with, I don't see it as inherent to dominance.
There was a time when I thought my whole dominant streak was an expression of a more masculine side of me. This could have been a version of ultimately self-limiting internalised misogyny, could have been fuelled by fear of being submerged by the stereotype or - a charitable interpretation - a profound (and to certain extent, a true yet very arrogant) sense of being apart.
I was wrong. This was proven to me when I played with a man who (for his own reasons irrelevant to this post) liked to call me "Sir" and, occasionally, "Master". At first, I was delighted by the idea and its application. But soon, it started to grate with me. I felt that it eradicated something of me, not unlike FSF would. It felt like submission despite my gender rather than because of it: not as bad, perhaps, but still not quite right. We eventually settled on a limited use of those gender-subverting terms - enough to keep both of us happy if for different reasons, but I learned a lot about how my sex/gender and role interact for me.
I happen to be a woman. I often like being a woman, I like having a female body and I enjoy some aspects of being (wonkily, but still) socialised as a woman. I want this recognised rather than put aside in any D/s dynamic.
I want to be submitted to as a woman. Not despite of that. But definitely not because of that.
My sex/gender is not the source of my dominance. And the assumption that it is turns me off. Not just sexually, but literally: it turns the 'me' off, eradicating it in submission to the fantasy hierarchy which only incidentally places me in the position of power. And even in fantasy, I don't want to be a mere functionary of a hierarchy, even if the hierarchy is one of Universal Female Supremacy.
If rigid power structures make your dick hard, and if you'd rather fetishise than subvert them, YKINMK. In a Female Supremacy world I'd probably be a sub.