I had the tiny dialog window problem and found a quick fix. I'm on a windows 10 laptop, and went to display settings. Under "scale and layout" I clicked on the dropdown menu for "change the size of text, apps, and other items" and changed it from 150% to 100%. Everything on my screen now looks small, but the paypal message center sizes correctly. I figure I'll just change it back when I'm done. Hope this helps!
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