Ahhh, finally figured out what I keep doing while reading Kindle in bed that changes the font size: pinch out to make text bigger; pinch in to make it smaller. That’ll save me a tedious trip to the menu bar next time I accidentally mess up the size.

@Cheri Heh, it's driven me crazy for way too long — lying in bed reading and my hand brushes the screen then suddenly GIANT TEXT. I've been meaning to look up what happened for the longest time.