Button set checked property not set on the highlighted radio input in Firefox

[Louis-Philippe Perras]

The issue can be reproduced with many versions of Firefox but I did my last tests using Firefox 47.0.1. Here are the steps to reproduce the issue:

• Navigate to the jQuery button set sample page. (​https://jqueryui.com/button/#radio)
• Launch the developer tools.
• Select the iframe ​http://jqueryui.com/resources/demos/button/radio.html at the top right corner.
• Type this snippet in the console and the value returned will be true:

  $("#radio2").prop("checked")
  

• Click on "Choice 1".
• Type the same snippet as before in the console and the value is now false.
• Click and hold the click on "Choice 2", then move the cursor from a couple of pixels before releasing it still over the "Choice 2" button.
• Type the same snippet of code as before and it will return false even though the button "Choice 2" is highlighted.

[Scott González]

Duplicate of #9990.