Solved Firefox saved login that's not mine.

Ok so I use firefox to save logins and password, For one site I have two or three different logins, but a fourth one has appeared that is definitely not one set by me. And I can't seem to remove it. The username isn't an email address - it's a long string of letters and numbers, and so is the password. At first I thought maybe it was a mistake saved login - ie if I had my finger pressing down or something and repeated keys. But the fact it can't be edited or removed makes me think its suspicious.

So as removing it did nothing, I tried editing it and changing username and password to null and null. It just reverted straight back again.

Any ideas? Is this a dodgy spam or malware thing? Or just firefox malfunctioning. The logins are to my own website.

It's ok. I cleared the browser cookies for the site and it disappeared again. But still very odd ..........