See https://en.wikipedia.org/wiki/File:Cite_dialog_with_large_boxes_for_fields.png
This is intermittent and may be relate to zooming in/large text size. The fields go back to normal size when you click inside them. Seen in both Firefox and Safari on Macs.
Today, I'm getting pretty consistent results by opening https://en.wikipedia.org/w/index.php?title=User:Whatamidoing_(WMF)/sandbox&veaction=edit in Safari and selecting the infobox. Opening it (double-clicking) the first time works as expected. Cancelling it (escape key) and opening it again produces larger than necessary fields.
Version: unspecified
Severity: minor