This question already has an answer here:
- 'innerText' works in IE, but not in Firefox 15 answers
document.getElementById('passwordinfo').textContent=''; //For firefox
For more info click HERE
innerText is not supported in firefox. Instead try innerHTML. Let me know if that works.
You also could use the html attribut reguired (explain) wich is supported from the most major Browsers (only Safari not) to check the user input. For the email validation you could use the type=email propertie (explain) to validate the email input which hase the same support as the required attribut.