Try browsing categories of media on the mobile web site − such as this example on Wikimedia Commons on 720px ( Samsung Galaxy S5 mini.)
With a big screen, five images are displayed per row. If reducing, this wraps to four images (good so far), and then to one image per row, even though there is a lot of space available − see attachment.
This makes it very hard and ugly to browser Wikimedia Commons categories.
To improve rendering in this browser and other similar devices I would suggest we switch the threshold for tablets down to 720px.
Reproduced under Chromium, Firefox, and Firefox for Android