This was Becca Meyer. My friend Eric, a wonderful father, lost his daughter today to anaplastic astrocytoma, an aggressive brain cancer. It was her 6th birthday. This should not be permitted.
The way to make the viewport in Firefox resize below 400px is to disable the navigation bar.
The way to make the viewport in Chrome resize below 400px is to dock the Developer Tools to the right. Or, use Chrome Canary and resize in the Override Device Metrics feature to set the device size.