Thanks for the great feedback! I think all browsers are supposed to submit the form to itself if no action is defined. This is really interesting because this script hasn't ever had an action attribute, and we've been using it without any changes for probably five years or more. It boggles my mind that no one has reported this before. Did browsers change the way they handle actionless forms? Did everyone just try another browser without mentioning it for so many years? Either way I added an action atribute. Let us know if it works better in all browsers now. That still doesn't seem to work, so the action attribute was not the problem. Because the form is not submitted in some browsers, it must be a problem with how the submit event is handled. The form itself definitely worked before in FF, but I think the script that is executed onsubmit is new, right? I've experimented a bit and found that onsubmit="submitFunction" seems to work (though I have no idea why the current code doesn't). Other variants (e.g. with return true) also don't seem to work. However, apparently then the code for the loading screen won't be executed at least in FF. That sounds pretty weird, but I think most developers now use more modern APIs instead of the onsubmit attribute to react to submit events, so they wouldn't run into these issues.