Progress Example submit button stuck in disabled state on Firefox

It is possible to get the submit button on the Progress Example page stuck in a disabled state on the Firefox browser.

To reproduce:

1. Go to http://build.fluidproject.org/infusion/demos/progress/ in Firefox
2. Click the Submit button
3. Reload the page using the browser's reload button

Expect:

• The Submit button is enabled

Actual:

• The Submit button is disabled