Earlier today Apple mistakenly started signing older firmwares. This is a mistake and Apple will most likely correct it in the next few hours. This mistake, however, allows users to downgrade to previous iOS versions and even jailbreak their devices. The list of all the current and older firmwares signed by Apple is as follows:
iOS 10.2 <— BEST PLACE FOR iOS 10 JAILBREAK
iOS 10.1.1 <— BEST PLACE FOR iOS 10 JAILBREAK (iPhone 7)
With these firmwares being signed you can save their blobs for future downgrades. The process of how to do it is shown in the video below – (The following process uses Telegram bot to save blobs)
Update: Apple has stopped signing older firmwares. Big congrats to those who were able to downgrade. Those who couldn’t, hard luck.