If you enable the 'Apply AutoFit when page loaded or browser resized' setting, then by default AutoFit zoom will be applied to every page. However, if you then change the zoom level for a specific page using the toolbar button popup, that zoom level will always be applied instead of AutoFit zoom whenever visiting that page or pages from the same site. If you later click the 'Reset' zoom button while on that specific page, then AutoFit zoom will be applied by default.