Tried the old version and the new one. Works fine in IE. In Firefox, after pressing the send button, the page loads again, but the message does not get posted to the seller.
Just saw that there is a subforum for bugs. I guess it really belongs there.
Firefox, in my experience, has proven to be generally weaker or iffy on “forms” for several years now. Forms (free-text reply boxes) sometimes work and sometimes don’t. Depends on the sites, the day, the relative humidity, etc. But is better than other browsers for some things, so it is a tradeoff. Use it if it works – have a backup plan for the times it doesn’t.
Also, the “Bugs” section of the Forum is oonly visible to customers while they are logged in as a Forum customer. If you feel like posting a topic that EVERYONE will see, logged in or not, the “BUGS” section may not be best.