After some contentious (and personally upsetting) arguments about some trans-legitimacy issues with an old friend on FB, I decided to come out to her in a PM explaining why I was going to have to leave the conversations. It was the first time I've really gotten anti-trans type attitudes from friends, so I really had second thoughts about whether to come out or just drop the matter and go silent.
The result was a really rewarding conversation in which she shared some pretty personal experiences that went a long way toward explaining her perspective (which turns out not to have been as anti-trans as I'd taken it to be) and she made it clear that she would be respectful and supportive when I do transition. I came out of our conversation feeling a closer connection with her than ever before, and it really felt good to feel at peace instead of harboring the stress of FB strife that had been with me for the last week or so.
It made me feel, once more, impossibly lucky, because even the "anti trans" people close to me are actually trans-friendly...