Issue reported to the bank to. If you open the website and see access work from mobile firefox on android than maybe problem was already solved by the bank (finding other code work for firefox)

This is an issue with the bank. The content type that is sent is "application/vnd.wap.xhtml+xml" which is not a valid mime type.

I opened https://webcompat.com/issues/405 to track the bank fixing the issue.

Thanks kbrosnan

peopleinside said

If I press "Accedi" on the mobile version of the sella.it Italian bank website (opened from mobile devide Samsung Galaxy S5 witf Firefox), the log-in page is not showed but downloaded - is an aspx page and is downloaded from Firefox not opened. If I open the website from other mobile browser this issue not exist. Firefox from mobile devide, mine is Samsung Galaxy S5 the issue i see in Firefox for mobile on Android Samsung Galaxy S5 Android 4.4.2