Top-down field entry at a web site resets to first selection every time.

Site URL: http://www.surepayroll.com/calculator/calc_paycheck_netpay.asp I enter the state field (top-down selection). It resets to the first state instead of remaining on the selected state. This happens in firefox for windows and in the Linux (I run Ubuntu) version. It DOES NOT happen with other browsers (Chrome in particular - it doesn't happen in IE11 either). I tried doing this with add ons disabled (from the help tab). Same results. So I suspect an add-on is not causing the issue. However my knowledge of Firefox with add-ons is limited. I obviously cannot eliminate a site issue as I don't have a connection with the admins of the site. Should I pursue it there (if possible)? I don't see what else I can do at this juncture. Have saved a dump of the troubleshooting "sheet" or firefox troubleshooting dump (text file) and a screen capture of the page in question in a .png file. If you want this material/data let me know. Thank you. Best contact is email for me. I check it frequently when I am at the computer.