This is a continuation of an issue I had in FMGo14 which had a workaround: Issue with web viewer text size on device rotation.
I tested in FMGo15 and the behavior has changed. The text is always enlarged in the web viewer. The text size cannot be reset. This is a big UI problem as a web viewer containing text with no interaction (scrolling) allowed and designed to have a static size on the layout increases the size of the text but not the containing web viewer object. Only the text inside the web viewer is scaled up. On devices like phones this is not a happy thing.