Sorry you are having trouble! I wasn't able to replicate that issue using firefox. Sometimes different browser extensions can cause unexpected site behavior. One thing you might want to try is temporarily disabling any add-ons or extensions you have installed to see if one of those (or a combination of them) could be interfering with the functionality of the site. If you do that and find the site works, then turn them back on one at a time until you discover the culprit.
You can also try clearing your cache and cookies as well as making sure you have all the latest updates to Firefox.