Inspired by this: https://support.mozilla.org/en-US/questions/1462048.
Here we have a new user who is struggling to see the icons to the right of the Address Bar. I was surprised that Firefox doesn't seem to have any sort of Accessibility settings.
I'd suggest some sort of High-Visibilty Mode where the icons in question would be as tall as Address Bar itself and show solid rather than as outlines, even, heaven forefend, be colourful — even if you can't see it you'd soon learn when to click the red/green/blue blob. There would also seem to be sufficient room for the icons and labels on the bookmarks bar and in tabs to be bigger, though the latter would ideally be made longer to compensate. Obviously this would mean space for fewer tabs and bookmarks but I think people would rather have fewer and be able to see them.
It is possible to make the everything bigger but that involves about:config. Surely it wouldn't be too huge a task to add a setting for that along with the web-page Zoom in the normal settings if resources aren't available to do something more involved.