I work with three programs on the screen in parallel and should be able to reduce the resolution of FamilySearch to 75%, for example. I don't need such large fonts.
The zoom level or magnification is controlled by your browser and operating system; in Windows, ctrl-minus generally works to reduce it.
You can change the resolution in your browser(s) and/or in your monitor settings.
Sorry Julia - your reply wasn't yet visible when I commented.