Why does clicking on the Firefox button or right-clicking bring up either a very small thumbnail or a zoomed in view of the menu options?

Whenever I click on the Firefox menu button or right-click on a hyper link within the broswer, instead of a menu of choices, I am presented with either a tiny thumbnail of the page I am on and the menu expanded (also very tiny). After moving the mouse, the thumbnail disappears and becomes a hyper-zoomed display of the menu that should have displayed. The zoom really looks like what an assistive-reading display would look like.

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