Maybe I should added that clicking next after putting my email address doesn't do anything.

Firefox appear to be getting a multi (two) page login form where you enter the email or mobile phone number on the first page and the password on the next (second) page. This works for me and I get a page to enter the password if I click Next, so in your case something might be blocking this HTTP request.

You can check the Web Console for possible errors and warnings.

• "3-bar" menu button -> Web Developer or Tools -> Browser Tools -> Web Developer Tools
• https://developer.mozilla.org/en-US/docs/Tools/Web_Console