I am guessing you are all using Firefox to log into NMP........this came in when firefox updated last, which it would have done in the last week or so... mine updated tonight.
NMP not beng a 'secure' site just means that the information such as your password is not encrypted so yes potentially your account could be at risk BUT NMP does not hold any of your important information, no credit card number or bank card number, no address and not even your name... the only thing personal to you that is on your NMP account is your email address so I am pretty sure no one would actually want to 'compromise' your login on NMP. I am pretty confident NMP is safe....
The scurity cetificate costs per month or per year which puts more running costs on to NMP which at the minute Nic really cant afford.... as I say I am really quite confident that NMP is safe without it as there are no details held on your account.
if you are worried then maybe you could change your email address on your account to one which isn't your main email address....... but to me there wouldn't me much point as it is something which is very very very unlikely to happen!
here is the page explaining the update to firefox.... https://support.mozilla.org/t5/Prote...fox/ta-p/27861