Rendered animation very small

Fedora 31 KDE spin, all patches up to date.

Using Firefox 75.0.  Problem also appears in SeaMonkey 2.53.1

Flash version 32.0.0.363

GPU is GeForce GTX 1050

Monitor is 4k, but resolution reduced to  3480x2160.

When rendering the page at https://radar.weather.gov/radar.php?rid=FCX&product=NCR&overlay=11101111&loop=yes , the animation appears very small.  It should fill most of the blue panel, but as you can see in the screen shot attached, it only fills about 25% of the area.

This works correctly on other computers on my same home network running the same software (although with lesser monitor/GPU)

Kindly suggest options