Well, in spite of being a member in good standing of the I Hate Melisandre club, I certainly wouldn't put it past her, but in this case I really don't think she started the fire. I don't doubt her ruthlessness or her manipulativeness at all, I just don't think she's the culprit here. She obviously does have magic and some sort of inner 'alarm system', but it seemed to me she came outside the tent simply because she sensed something was amiss. I thought she genuinely looked confused, then frightened as she realized what was happening. (Plus, we already knew Ramsay was on his way with 20 men who surely would have thrown the torches from horseback, being far from the tents when the tents caught fire. Part of Ramsay's strategy would of course have been to have his men surrounding the camp, giving rise to fear in Stannis's camp that they were being attacked from all sides at once.) The poor horse (horrible! I had to do the 'la la la la' through that) was obviously, IMO, hit by a torch that was meant for a tent.
I, too, had the sense that somehow Drogon sensed Dany's danger, similar to the time he showed up because he sensed she was so discouraged and conflicted about how to rightly rule. In the books, it was the smell of blood that drew him, and I think that could very well have been the case here, too, perhaps heightened by the bond and 6th sense Targs share with their dragons. I don't have any sense that Targs can warg their dragons, though, and that's not something that's been supported in the books so far. (Plus, she didn't do that roll-y eyes thing that Bran always does, and that Orell did -- thank goodness. That stuff creeps me out a bit. )
I had been convinced that Hizdahr was the Harpy, but this episode sure put the nix to that. I believe now that it will be Daario, the last one to betray her as prophesized, and I do think it will be Tyrion who sniffs him out.
Although I originally rated it a 7, I think a good bit of that was because Shireen's sacrifice simply cast a hell of a black cloud over everything else that happened, even Daznak's Pit. Such clashing juxtaposition, it was hard to be excited about Drogon appearance while the cries of one of the sweetest, most generous and kind hearted little girl's screams were still echoing in my mind. The next time I watched it (FF through the Shireen scene), I thought that I would have rated it an 8 if I'd just waited. Next day I watched the Daznak Pit sequence by itself and that time, it brought tears to my eyes.
I thought Dorne was really pretty good (unlike any previous episodes), and I'm anxious to see what dynamics the presence of Trystane and Marcella create in KL. Can't wait to see Cerise's reaction when she encounters still one more thing she can't control. Would rather they have waited on The Wall until the final episode, rather than just showing such a brief couple of seconds about it. Really glad to see Arya out and about again, also am totally sure that she doesn't have Kindly Man/Jaqen fooled one bit. Anxious to see her reunited with Needle next week.
My sense is that it's only contracted when greyscale touches flesh directly. We just don't have a lot of information about it, though, granted. The stonemen whose touch had to be avoided at all costs, else the greyscale would be contracted, were pretty much greyscale from head to toe at this point, so it makes sense that any touch from them would cause contamination. Shireen's greyscale was not a threat to anyone, I'm guessing because it had been 'arrested' by whatever means through the masters Stannis brought in from all over the known world. I seriously doubt that Jorah would have put Dany at risk by offering her his hand in Daznak's pit if that meant that she would contract it.