How to set the zoom out or in for all pages permanently?

I wish to set my page size one size smaller than the default. The result of ctr - (zoom out) is exactly what I want (it decreases the size of text AND images). However this effect only lasts for the page I am currently on, as soon as I navigate to a different page (or just refresh the page I am at), it reverts back to the default size. I looked at Tools->Options->Content, however that deals only with text size (besides it looks only certain pages are affected by this setting anyway). In other words, how (or where) do I set my browser to automatically decrease size or 'Zoom Out' for all the pages I visit in order not to set it manually for every page every time. Regards PS. If this setting can be applied for individual users (I have a multi user PC) that would be even better, although I would be very grateful if I could just set it. PPS. Additional information. I just discovered it seems to be working now in normal browsing but not in private browsing, my apologies for the omission.